An OC can as long as you make their back ground that of a Panem native. But we encourage OC mentors! For example notfunandgames is an OC mentor. If you go to the last section in this page you can see which slots are open.

Because all of the multifandom games where they are bringing in tributes from other worlds are being played in game and have an ingame winner, a character from another world would have to play and either win or prove they are worth more as mentor than a tribute to not be in the games.

Did that cover it?