Maybe you can implement CoinSwitch so users can deposit something like 300 different currencies. I think this is way more easier to implement that every coin seperately.
Whats the point? If someone has dogecoin and deposit dogecoin into this site, that means the player wants to gamble with it so there is no point in using coinswitch. Imagine that you have bitcoin then you switch it to dogecoin just for the sake of gambling with it, whats the point of it if you can gamble with your bitcoin directly ?
Of course if someone wants to gamble in the currency he got it's no problem. The point is that when you want to implement multiple currencies this means you got a lot more effort maintaining those currencies.
They can still implement other currencies but if they have implemented Coinswitch they can also attract players with currencies they don't support.