"IF" is a very risky thing to hang your company's public image and future sales on.
Again, this isn't about Michael Vick. He's going to be alright, because the sports industry has re-inducted him into their ranks. He'll make money, that's assured.
But, any company who commits to being his business partner is rolling the dice that it's going to work for them. Personally, I wouldn't take that bet.
Nike is rolling loaded dice.