Overall, I think the UFC has been pretty fair to their fighters. They took a huge risk with a large investment in the beginning. The shows and PPV aren't cheap to put on.
Without a doubt, the UFC has done more for fighters than all other MMA organizations combined. Because of the UFC, MMA is a much bigger sport, with more opportunities and a lot more money for the fighters. They do a good job of taking care of fighters with bonuses, health care, etc.
That said, because they have a virtual monopoly, and because Dana is such an emotional little biatch, there are fighters that get fucked. If you don't play by the UFC rules and/or get on Dana's bad side, you end up like Shamrock, Ortiz, Torrez, Rampage, etc.