That's why lately I've shown interest in making non-student OCs - to show there's a whole wide world out there and the the fairy tale community involves lots of different people. I especially like making non-student OCs that have no connections to any student OCs.
As for AUs with other people's OCs...a lot of people tend to get defensive at the idea of someone else using their OC. I can understand, since to many creators, only they can truly understand their characters. This is why some authors hate fanfiction, or at least refrain from reading it. A handful of authors, like Anne Rice, P.N. Elrod, Robin McKinley, and Terry Goodkind, have even asked FanFiction.Net to not allow fanfics based on their works, and FF.Net respects their wishes.
Fan works are actually something to be careful about in general, since there have been incidents where fans have gotten into trouble because of their fan works. Companies and individuals can sue people over unauthorized use of their characters. For example, if I owned a clothing store and made and sold a bunch of Pikachu T-shirts without Nintendo's permission, Nintendo could sue me and would definitely win the lawsuit if they filed it. If you made a fan movie about Draco Malfoy's post-Hogwarts life, J.K. Rowling could sue you. YouTube has taken down millions of videos due to copyright claims. However, keep in mind that it depends on the type of media and the context. Disney would not go after someone's fanart of Elsa or an Olaf puppet that someone made for their little brother, but they would likely go after unauthorized Frozen merchandise or a Frozen fan movie.