The importer should be eventually able to import these. There are some limitations of what can be imported, either for technological or performance reasons, but generally yes - though it will have to be tested.
I don't know about the license, but it's possible that you'd have to obtain the rights from the owners, I don't suppose they gave the right to use to Google and to anyone else, so it may be a problem even if Google itself allowed it.
We can, eventually, make the user be responsible for the legality of his submissions. We need to look at Second Life or some such, how they are dealing with user created/submitted content that may be problematic. Especially if the platform allows to sell stuff, from players to other players, or when the player created content can become a part of the game.
