Yes it does

Yes, you can add beast forms to your Wild Shape repertoire of beasts seen by casting conjure animals. The spell explicitly says the conjured creatures literally are beasts, and a creature of the type beast is all Wild Shape needs you to see in order to add its form to your repertoire.

Though someone might by tempted to quibble that they're not real beasts because they're really fey spirits clothed in the shape of beasts, look at it this way: First the Druid conjures a bunch of spirits that take on the form and behaviour of the real beasts they look like. The creatures so conjured proceed to behave and look exactly like the real thing. What better opportunity is there for a shapechanger to learn a new form to wear, than to see a nature spirit do the exact same thing as they're wanting to learn to do?

But it's of limited use

What you might actually run afoul of is limitations on metagaming, or a DM whose setting doesn't include just any creature you can think of (even if it's in the Monster Manual).

• A DM who wants to limit metagaming would be within their rights to ask you to justify your choice. If you try to summon a Giant Owl but your druid has never seen one before, a DM could easily say "How do you know those exist? You've never seen one. How is your druid "choosing" an animal (s)he has never seen or heard of before?"
• A DM who has developed a custom setting isn't straightjacketed by the Monster Manual and doesn't have to include everything in it. Giant Owls might not exist in a DM's campaign.

This also means that this is much less of a loophole than it might seem — after all, how big is the difference between the set of creatures a druid has personally seen and the set of creatures the druid knows about well enough to deliberately try to conjure? I can't imagine it's a very large number.

But in principle, yes, a conjured animal inhabited by a fey spirit is plenty to learn that form from. Just mind that, if you can conjure a particular animal, it's highly likely your druid has already seen it anyway. This makes this method of acquiring new forms both limited in utility and not much of a loophole to worry about, either way.

Yes, but the game doesn't tell you which. As long as your Druid isn't a newborn baby, they've likely seen some beasts in their life (especially during and after their Druid training!), and therefore can Wild Shape into those beasts.

Your background is probably the best guide to what creatures you've likely seen, as your background will imply a region that's familiar to you. Any beast common to the region in which you grew up and trained is a beast you've likely seen many times, and uncommon ones are likely to have been seen once or twice too.

This is all between you and your DM, of course, because the game doesn't rigidly define a list or rigidly define a way to create one. You're two reasonable people who enjoy playing games together though, so I'm sure you'll figure out an enjoyable, reasonable set of beasts that you can agree makes sense for a nature-loving outdoorsy person to have ever seen in their life.