Went out there for the Partizan game in the EL a few years ago. I think there are some good groups out there among the smaller teams, like Zemun or Vojvodina. Yes it's true that I'm talking 400-500 people, but top quality support. Go and watch Zemun or OFK or someone like that play, it's basically just their ultras there (unless, as you say, they are playing one of the big two). Shit football, stadiums that are falling down but a small hardcore of fans who would die for the club.
Most people are gloryhunters I agree. Partizan and Red Star also very good core supports (not the gloryhunters). Everyone is right-wing because it's Serbia! I don't agree with their politics but I admire their proper supporters.