Its fine as long as monetary exchanges are forbidden.
You can allow sig bets, maybe even bets for charitable donations, but not actual money exchanges. Individuals can do that on random threads while you look the other way, and you're fine -- but if you're going to set up a whole separate forum designed for "bets," where money can change hands -- and then play an enforcement role for non-payment! -- then you're in the gambling business. Whether or not you take a rake.
Lets try to make it through at least the first day before getting shut down by the state Attorney General's office, eh Willie? :]