Betcoin dice or SatoshiDice didn't work like that there was no withdrawal or deposit. You sent BTC to an address and then your hash got a roll, if you won the script would automatically pay it you with a tx back to your depositing address, the whole thing was permissionless and with no account needed, no deposits, no balance no nothing!
If they don't require any confirmation or if they don't have any deposit or withdrawal option, then there is a high chance scammer may scam them by double spending. I have never used these sites, so I have no idea about them. But my question is, if anyone misuses the double-spending option, then how can they prevent being scammed?