. . . I create a wallet for each outcome . . .
Be careful about your terminology. There is no need to use two "wallets". Nobody can determine how many "wallets" you are using, so using one "wallet", two "wallets", or ten "wallets" isn't going to make a difference. What you seem to be suggesting is using two different "addresses", and yes if you publicly advertise which address is associated with wager, then the blockchain will provide a method for proving the total number of bets placed on each outcome. Since the wager "addresses" will be publicized, there isn't a lot of benefit to combining the balances from the two addresses into a single address before paying out winning wagers. The winners can simply have their initial bets sent back to them, and their "winnings" paid to them directly from the address that represents the "losing" wagers. If you really want to increase the visibility of the connection between winning and loosing wagers, you could create a single transaction to pay all winners. The transaction would take all of the wagers from both addresses as inputs, and then have an output for each and every winning payee.