Truthfully, a lot of times, this type of RP seems more like "But I want to be original or go against the grain" rather than good RP.
I want to the Jedi class, but I want to be a Sith Background! Also, it makes for harder things, like "Now you're exposed! Everyone knows you're really a Sith pretending to be a Jedi to infiltrate them, but you ignore it because it ruins your game." ect ect ect Basically things like that.
Only if you're blatant, I wouldn't even say my dark side Jedi is sith, merely a dark jedi. it also really depends on what part of the story line you set the roleplay in, if the treaty is still enforce, then a diplomatic figures from the Empire assisted by guards would be fine.
The problem I see with current rp is there's no protagonist and antagonist, it's all "good" people conversing among themselves, so while the idea of the "enemy" being around is a bit peculiar I think it's necessary for a good to and fro type of rp.