Yeah and then, how much success in MMA do they have to have had?
Roger is the best pure grappler I've ever seen if you combine gi and no gi. The best version of him is the clear cut #1 seed in any openweight gi tournament you could draw up. And he's at or near the top in a no gi tourney as well. And he's had SOME success in MMA. But then you have Maia and Jacare. Maybe a half step down in grappling accomplishments than Roger (I mean, they are close, but still just a shade below him) but have had more success actually inside of MMA. And then you have Werdum, another rung down in terms of grappling accomplishments (though still extremely decorated) but with even more success in MMA.
Then guys like Mir and Nog who used bjj extremely effectively in MMA but really weren't as decorated as grapplers outside the cage (hell Mir not at all, he stopped even training for pure grappling when he got his purple belt so he could focus on MMA).
The question is pretty ambiguous. Depending on how you view it, a lot of answers "work".