the slots are way too big as currently envisaged - $50. all the most sensible slots would get snapped up very quickly
smart contracts are not a thing in bitcoin.
can there be script that executes such a contract? if not then we would have to have an escrow or mic or me are doing this.
no. it's totally unrealistic at this stage. maybe Augur or something is working on that sort of thing but it's not safe and not necessary.
escrow is fine and proven
further thoughts - you might have to pay the escrow
actually keep the number of entrants small, keep it down to known forum entities, otherwise you will have to have address signing.
people may be more willing to take part if a % of the pot goes to a charity