It means "to do" here. It's the colloquial verson of する. My guess is that this means something like - A person who wants to do/is intent on doing something will do it anyway (even if it's wrong or in spite anyone trying to stop him/her from doing it, etc.). Example: 「禁止してもやるやつはやるだろう.」
I feel it's close to "Those who can, do", in nuance. (literally those who do, do). Like, you're either やる奴 or やらない奴.
sidenote: やる can be "do" in a lot of senses, and is also sometimes used as a translation for a versatile four-letter English verb starting "f". This fact has been responsible for some of the funniest Google translation errors I've ever seen.