If you have a competition and someone wins then you are obligated to pay them out whatever was offered as a prize. Unless it's something ridiculous or illegal of course.
Well that would depend on your jurisdiction. Sythe.org is not involved in any gambling. It is purely between the participants of the game. We are just providing a mode of communication for you.
That said, I'm sure holding a raffle among your friends isn't illegal where you are. And if it is, just use bitcoins (not a 'real currency' according to every major government) and avoid the whole mess of legislation.