Only what I think is that the gambling sites can make the same network addresses for such coins instead, this is what exchanges do that make such mistake not to be common. Mistakenly used Ethereum network instead of using Binance network should not easily lead to loss of coin. I can not use such gambling site.
If the casino doesn't usually have bad intentions, I don’t see any reason why they would stress themselves out by creating a separate wallet for each MEW-compatible network when one can do the job. Even after doing that, they could manually credit the deposit to the user if they wanted and ask the person to pay for the extra hassle unless they actually used that method to steal from customers, despite there being a warning sign against such on their deposit section.