Sean Obasi, I think is the dude's name. He's a pretty legit Wing Chun student, and has won a few MMA fights if I'm not mistaken. Mind you, what he did in those MMA fights to win looked very, very little like Wing Chun. He also made an absolute fool of himself at some tryouts for a major organization, but I can't recall for the life of me the name of the organization. The biggest Russian one, or something? I don't know. His meltdown at the tryouts are on youtube, for the world to see.
I also seen some other video of a Wing Chun fighter sparring with a kickboxer and dominating pretty well. As for them being at an equal level, I don't know. I would guess not, but that would be a guess.
I wouldn't rely on any one martial art for MMA though, or in general. Current state of traditional martial arts means that to be a well rounded martial artist, one needs to cross train.