You will not find any one in the UFC who claims one style as his own. Chuck Liddell has a black belt in Karate. I'm sure he has incorporated some of that Karate training into his overall style when he throws his occasional kick. As for TKD, I've seen the reverse back kick work in the UFC and that is taken from TKD. Pretty much every martial art has at least some moves that would be effective in the cage.
I think the problem with something like Kung Fu is that the moves are too complex for most people to pull off with the speed necessary to use in an MMA environment. Personally, just using my jab and cross, I can throw out about 4-6 punches within one second. Straight up boxing style punches are very effective AND quick. A Kung Fu guy may be able to hit hard with his complex kicks, but you can see them coming from a mile away unless he's very fast. Plus the Kung Fu stance doesn't work well in MMA, neither does the TKD stance. Both have the fighters sort of turned to their side with their weight on their back leg. TKD punches are horrible(I too TKD in highschool), sh*t like punching from the hip. Straight up wack.
I have seen at least one style of Kung Fu that looks pretty damn impressive to me, Wing Tsun:
http://www.youtube.com/watch?v=ZM676yGD_5w&mode=related&search=