I agree with Sephex. Of course it's possible that the guy in the pipe is Zack. You could defend that position forever. What? Zack got shot in the head at point blank range? But it's possible that the Jesus Christ came down from heaven and healed Zack.

The point being, this debate is pointless. I mean, you're arguing about what sound the lid of a coffin makes when it hits the floor and how full Vincent's limit break was when you get him. End this already.