For the Rebel Legion, the link below is where you would go to find a list of most of the acceptable costumes (there are other accept costumes that aren't listed, like some face characters and comic book costumes, so the list is by no means only what is acceptable)...
http://www.rebellegion.com/costume-standards/full-costume-list/To navigate it easier go to Get Involved -> Costume Standards -> By Category or By Source.
And for the Rebel Legion you don't actually submit the your costume to a liaison, you submit your costume pictures via a link on the RL forum and a costume judge will look it over. There are different sets of judges for different sections... For example, I'm a Rebel pilot judge, and I judge Rebel pilot costume applications (X-wing pilot, Y-wing pilot, snowspeeder pilot, B-wing pilot, A-wing pilot, Biggs Darklighter, Jek Porkins, and so on... And the Resistance X-wing pilot costumes in the near future, too).
Satele Shan would, for example, but a Rebel Legion costume. As would a generic Jedi. Or an X-wing pilot. Or a Rebel Fleet Trooper. Or Mon Mothma. Chewbacca, Han Solo and Lando Calrissian. Hera, Sabine, Kanan, Ezra and Zeb from Star Wars Rebels would also be Rebel Legion costumes.