In addition, do not forget about the execution time - usually casinos require several confirmations, and I think that in modern conditions it is irrelevant to wait for a transaction to be completed for almost an hour.
Afaik most casinos only require one confirmation on bitcoin deposits and sometimes there are other casinos that require a few more for withdrawal requests.
I rarely play with altcoins but I think they're the ones that require several confirmations since the block times are much faster.
IIRC, there are even some casinos that do not even require a confirmation on deposit, they'll just credit right away once it's already in the blockchain, but during withdrawal, it should be confirmed before they'll process it. It usually requires 3 confirmations for bitcoin and it's alright because they have a good feature which credits your deposit without confirmation. However, I think there are only a few sites that do it now because it's a bit risky on their site, maybe 1 confirmation is a bit safer.
No confirmation deposit is no more or cant really be seen on most gambling sites today and i dont know what gambling site you are preferring or talking into because most of them
does require at least 1 confirmation or depending on the site.
Risk of multi-spend is there if they do set out that no confirmation deposit and there are lots of instances that it do happen and majority of these platforms are much aware with that.
For withdrawals then its neither instant or manually processed.