I was about to post this but since you've already done so, I'll just give my suggestion. If he violates the contest rules, he should be disqualified from receiving any prize. However, if the rules don't mention it he still has a chance to win the prize (specially he submitted a great entry). I believe the decision should be left to the contest organizer and its participants but if you ask me whether he can still win the prize, I will disqualify him as he may have submitted a double entry in the contest. Once a cheater always a cheater.