I honestly think your suggestion in the question is probably the best route.
There are major pros for the players if they pick Bob up as an Aspect
If they have Bob as an aspect, it becomes a good way for them to gain fate points by using that aspect to stumble into danger, as well as giving you a pretty good way to introduce plot hooks. If they want to use Bob to augment their die rolls, they could spend a fate point to gain a bonus to whatever roll/reroll (I'd guess lore or something else applicable that's an applicable use of an aspect, but I can't quite recall). Once you've got them hooked on their new Aspect, take it away, and toss them a plot point so they can go get it back.
If they don't grab him as an Aspect, well, you've got a plot device, but they won't be getting any fate from when he decides to throw them a bone.
Yes.
The books never explicitly say that the GM should or must tell the players the difficulty, but that's because it takes it for granted. (It really should say, because – as you point out – keeping players in the dark is just so normal for so many GMs.)
There is circumstantial evidence in the text that the GM is supposed to set difficulties "in the open", but they're scattered throughout hundreds of pages and can be subtle. The most obvious, undeniable one is on page 311 of Your Story (emphasis mine):
Difficulty as Plot Device
Sometimes, assigning an unexpectedly high or low difficulty to an action can create an interesting detail for your game. For example, if the PCs are breaking into a small company’s office building, they probably expect most of the locks to be Good difficulty or lower. Finding one that’s Great or Superb difficulty would be unexpected, and this will serve as a flag to indicate that not all is what it seems. […]
Likewise, if the same PCs are infiltrating a Mafia don’s safehouse and all the locks are Average difficulty, it should be an indicator to them that something is wrong.
Note that there is no way that this bit of GMing advice makes sense in a system where difficulties are kept secret. If difficulties are secret, they can't serve as flags that something is up. If difficulties are normally secret and the GM reveals only the "odd" difficulty that's out of place, then the advice straight up doesn't make sense because the players won't have any other difficulties to compare with; and the simple fact that the GM is suddenly telling them difficulties would be the indicator, not the actual difficulty. It would be less artificial to just say what's out of place instead of "indicating" or "flagging" with difficulties. This bit of GMing advice simply wouldn't be in the book if it wasn't simply assumed that difficulties would be played in the open.
So yes, this passage is just a bit of sidebar GMing advice, but it reveals the underlying context of a system that is written with the solid bedrock assumption that players will be told the difficulty of every roll they make.
On top of that, as you point out there are many disadvantages with keeping difficulties secret:
- It slows down play significantly
- It makes in-character strategising (which in FATE is done via Aspects) impossible
- Players have no way of knowing what their characters do know – how their own world, bodies, and expertises work
- It robs the players of narrative power in a ruleset that is designed to be hugely collaborative (and functions poorly when it isn't)
- Playing "guess what the GM is thinking" is almost never fun. This is particularly true in the case of Fate's core mechanic, since uncertainty about target numbers adds no suspense while adding lots of drudgery.
I asked Fred Hicks via Twitter if there is an official rule either way, and he responded:
fredhicks
@sevensideddie I think Fate works best with difficulties in the open; you say jump, they ask how high, and you tell them. :)
4:26 PM - 14 Dec 12
So this is as official as it gets: The game doesn't require anyone to play with difficulties in the open, but the designer thinks people should and designed with that in mind. That's consistent with the books: they don't have a rule for it, but they consistently, subtly, assume that you'll play that way.
In sum, playing with secret difficulties is like voiding the warranty. You can do it, but the game is not guaranteed to perform as designed if you do. As you're discovering (and as I hope your GM can begin to appreciate), this game you're in is suffering somewhat for having its warranty voided and isn't operating at full capacity.
Best Answer
Your first question is about half a GM problem, and half a player/PC problem. I've been on both sides of this issue: GMing for a character who had little reason to participate in the story with the other PCs, and playing a character who had no reason to participate in the story and every reason to run wildly in the other direction. In both situations, the solution has two parts:
The GM finds ways to include the PC in the plot.
It sounds like your group is already doing this, but for posterity: this means that the GM must look for ways to actively involve the PC in the story, by using their background hooks, talking to the player about what the character might find interesting, and otherwise looking for ways to help the character find motivation within the story to participate in the story.
You do need to be careful not to change the story or the game's focus so much that the other players begin to feel excluded or ignored, but this is a matter of understanding your group, finding a balance, and getting buy-in from the player of the problem PC. Which brings me to part 2 of the solution:
The player finds ways to include their character in the plot.
This is the much harder part of the solution: the player must meet the GM halfway, otherwise the game becomes "The Problem PC Show!" and no one else has fun. This may mean the player has to bend or tweak the character in some way - not enough to compromise the core of the character, but enough to keep them with the group when otherwise they wouldn't stay.
This is, admittedly, difficult to do. Some people are so attached to their characters that they're unwilling to compromise; or they simply can't see a way to bend the character on an issue without breaking them completely. However, it's absolutely required in order to solve this problem.
Why player buy-in makes a difference:
When I played a character who had no reason to participate in the story, I looked hard for ways to make her want to be there. But all logic dictated that she run far away, find a hole, and pull it in after herself, so any other choices felt wrong to me. This showed in my roleplaying, and ultimately caused much frustration for our whole group as session after session became centered around getting her involved when she didn't "want" to be.
I put "want" in quotes there for a reason. Players with especially strong "my guy" syndrome (which I know I'm prone to) will insist that they're "just playing their character" and that "the character can't be changed". But when I GMed for a character who had no reason to be there, his player was willing to meet me halfway, and the result was a fun campaign for everyone where that character even made a large part of the highlight reel.
The reason it worked was because the player was willing to say, "he has no reason to come along, but does anyway, because that's how group-based RPGs work." We hand-waved it a bit as "he has nowhere else to go and nothing better to do", but really that character should have been as long-gone as mine wanted to be. But because the player was willing to take the meta option and bend his character enough to say "screw it, he's participating" without looking for a story reason, it worked. It kept the game from focusing too much on that character, but meant he was still there when story developments happened that he was interested in, thus giving him the time he needed to organically grow interested in the plot.
When the player isn't interested in the scenario
This part is a little trickier. If the player doesn't buy Dresden's world, including all the magic elements, what's he doing playing a Dresden Files game anyway? You and your co-GM need to talk to this guy privately, out of game, and ask him why he's playing. If he just wants to hang out with your group and doesn't care much about the game, then you need to address that. Maybe give him a character with a minor support role, so that he doesn't need to participate much in the game and can just hang out; maybe say that if he just wants to hang out, the game isn't the time for it and you'll find other group activities he can participate in. It's up to you and your group to decide what's best here.
If he insists that he wants to play the game, then you need to find out why he's actively sabotaging it. Tell him that his actions suggest he doesn't want to play, and in fact are making it harder to play. It's possible you simply have an attention hog on your hands, in which case you should deal with him appropriately. (I'd suggest going through the problem-players tag, as there are a number of questions and answers you may find relevant depending on your exact situation.)
TL;DR: The GM and the player need to meet halfway on adapting the character and the world. But if the player isn't buying the game's scenario in the first place, then that must be addressed first.