From MMA Scraps:

This disheartening bit of news first came from Golden Boy at the UG

I hear that all mma managers were informed that if any of their clients not currently under contract with the UFC..... sign to be a part of the EA game.......the will forever be banned for fighting in the UFC.

Sounds like a simple rumor right? Albeit from a pretty reputable source, but then later in the forum post, MMA Uber agent Ken Pavia of MMAAgents.com says this.

It's true. And they told me want the word out.

Even if this is true (which it appears to be), no other credible info has surfaced.  Who's behind it?  Will it be enforced?  What should up-and-comer fighters do - take money to be in EA MMA, or hold out for an invite from the UFC?  If Fedor appears in it, would Dana & Co. still pursue him?  This ukase could easily sink the rival game if too many people are scared away from agreeing to be in it.