There are a few MMA fighters that use Karate and Kung Fu as a discipline. For example Lyoto Machida and Roy Nelson. That doesn't mean those styles can be attributed to their success. They also train in Muay Thai and BJJ. For the most part, no one has really figured out how to make Karate and Kung Fu work solely by themselves in MMA.
a lot of guys use karate. to name a few: chuck liddell and gsp and a lot more. only 2 guys i know does kung fu and honestly i don't believe them. they are lorenz larkin and roy nelson