I really doubt that any fighter in the UFC has a guarantee of employment, either of a legal or practical nature. The quality of the UFC's fights depends upon the tenuous nature of the fighter's employment, and this formula has worked very well so far, from the consumer's/fan's point of view. (That is, the fighters are very well aware of the fact that their contracts and employment are on a hire and fire "at will" basis).
What was really enlightening was Dana's Q and A session broadcast on UFC.com the day prior to the card. Dana is very inventive, forward thinking and constantly eyeing methods of expanding the sport.
But the tradeoff is that 90% of their roster is paid next to nothing, and constantly under the thread of unemployment. If Dana and the Fertitta bros. paid more, they'd have less money for expansion, new signings, acquisitions (Pride for example), and so on.
I wish there were an easy solution to the dilemma of fighter pay and job security vs. MMA growth and excitement on the other.