I have also met some very strong vegans (they supplement, exercise, and eat nuts and lots of greens) and some very weak vegans (they are couch potatoes, eat tofu, potato chips and lots of processed food). In the end, no matter what diet you are on, the quality of food and exercise is everything!

Athletes eating meat, most certainly supplement also. I was in the Fitness and Kickboxing scene for a decade. trained and instructed. Lots of Sups, and a fair amount of steroids.. (I did neither, but thats because I've always been tight with $$ :P, and now tighter with my sats ;) ).