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.

I play a druid character who regularly uses conjuration spells. To make life easy on my DM I prepared a cheat sheet of all the summonable subjects. It's just a little sheet that has AC, relevant abilities and a hit point marker for each summoned creature. If there are 8 creatures summoned for that CR, then there are 8 hit point markers. He usually has me run them for him, but he still makes the decision. Each entry on the sheet has key words that can help him make a quick judgement call: underground, flying, darkvision, poison, etc.

When I cast the spell, I tell him what my character is hoping will appear, usually using a keyword. If I am hoping for air support, I might get owls, or bats. For poison, I might get snakes or spiders. Part of the fun of D&D is dealing with surprise results (one of the main reasons the game has dice).

So yeah, if your players intend on making a lot of use of these spells, some prep work ahead of time can be helpful. If you can convince them to do the heavy lifting (as I did for my DM) so much the better.

In general, the DM should make something appear that has some relevancy and helpfulness for the current situation. The player is expending a spell resource, after all.