I love both games and the thing about MMA is that it is a system that could easily be converted to a Role Playing Game format without much of a problem.
Newer RPG's like Skyrim have an amazing leveling system that would work brilliantly in an MMA game.
Your character levels through using skills. Specifically, if you punch a lot, those punches will level more, or leg kicks, high kicks, double leg takedowns, etc.... You can only level and master a move through continuous use so your character/fighter would level naturally as you play him much like Bethesda has tried to do in it's Elder Scrolls and Fallout series.
What if your MMA game was more like this:
You create your fighter for career mode and he has attributes, skills and styles.
These all have "perks" associated with them that you can choose to take as you level up and qualify for them so you can focus more on things like cardio, combination punching, one punch KO power, or whatever else someone dreams up for a game like this.
In this kind of game you have to actually throw and land a punch for it's skill to start rising, same with any other move although submissions should gain points based on attempts and/or length of time attempted as well as bonus for successful tapouts.
RPG's are designed to allow you to custom build any kind of character from a juggernaut tank of a warrior to a slick, stealthy killer.
MMA is very, very similar, hell, it's a sport full of nerds. It's styles or classes with specific skill sets and moves within each discipline, break those down and you have an RPG/MMA game.
Of course it would be nice to make it more epic and allow you to travel to different gyms and cities and work up your skills through sparring sessions in different gyms, amateur or smoker events, grappling tournaments like NAGA or ADCC, boxing, kickboxing, whatever, let the character compete in all these things to build up their skills, experience and fame then utilize all these skills in the Octagon.
So basically, add a more epic scope and more playable character that we actively create and adapt and you will have a more playable and more importantly, replayable game that could in turn become something like an online MMORPG but as an MMA game with world wide rankings.
Just a thought.