The difference is they are not banning someone from ever playing in the NFL if they are in a video game they don't support. The athelete can still make his livelihood in the NFL.
This may actually backfire and end up helping other orgs, as there are plenty of up and comer guys out there who need the 5, 10, 15k or whatever they get for being in a video game.
You don't sea EA saying you will never be in one of our video games if you sign with the UFC. The comparison is completely unrelated. It's cross genre control of an employee/contractor and is just plain overcontrolling and monopolistic of the UFC. They can do it, but it will not work long term in their favor.
I'm not a fan of unions. They end up breeding mediocrity in the long run, but the fighters need one at this stage of the game. It would. actually do some good things