You can add TRX, Doge, EOS, Waves, XEM and XRP for the coin, which has a low transaction fee. But you can still use bitcoin, ethereum, litecoin, as many gamblers will still use those coins. Besides the coins with high transaction fees, you have the other altcoins, which can be convenient to most gamblers who want to avoid the high fee.
when you are on the platform and have deposited to it anyway, you don't have to pay transaction fees to bet, the only worries will be withdrawing the BTC or ETH.
the one that i use often is the TRON for cheap fees. EOS has a good way of doing things because the transactions are free as long as you keep some for the CPU and RAM for your wallet. someone suggested EOS before and upon closer look by using tokenpocket, a user will have access to gambling dapps and he can bet without having to pay fees.