I think for the most part fighters are fairly compensated with a few exceptions.
Comparing the NFL and the UFC is a little rediculous IMO. The UFC's revenue is probably comparable to a mid-tier NFL franchise.
For the most part NFL teams get to keep 100% of the gate/concession/parking. The UFC has to give a percentage to whatever arena is hosting them. Also the NFL receives a sick amount of money from their network deals, and it is a predetermined amount not dependent on ratings. The UFC on the other hand has to rely the amount of buys to get their money. And even then they still have to share some of that revenue with the cable companies.
Look at the companies that gave out huge fighter salaries (Pride, Affliction), where are they now?
The first rule of business is that the boss has to make his first. Right now the Fertitas and Dana are making some good money. Eventually that will overflow to the fighters.
It would be impossible to get a group plan for professional fighters, so fighters are required the self-insure. The UFC pays for any injuries that are suffered during a sanctioned bout.