Yes hacks are the biggest danger a casino could face.
But most of them are already storing 95% of their funds in cold storages or multisig wallets.
They can easily calculate how much BTC the casino pays to gamblers daily and only keep that much in the hotwallet, the rest can be kept safely in a cold wallet and only recharge the hotwallet when it's needed.
So if a hack happens they can only steal 5%, which is still bad, but better than 100%.
Good insight. In my experience being hacked is a concern, but only at the beginning with untested software. yes, you do go through beta testing, load tolerance etc. Hackers can always find a way. I've found that the could hack our systems, are the ones who are off doing better things than trying to grab small change (at least for them). There have been some successful hackers who have found very interesting and advanced ways to gain the system, but each time we learn. I honestly hope we don't' learn this much this year. lol.
About the hot wallet. Most players take their funds immediately after their sports bets win. We always increase the hot wallet after very large deposits, just to make sure that we are comfortably able to have the player withdraw funds immediately. Cold wallet storage is one of the advantages of BTC as the main currency.
I forgot to add the most important part. Investing in a casino (operators side) is ONLY a good idea if you have access to players. ie. affiliate websites, marketing strategy (PPC, affiliate program etc). Starting off without the knowledge is very difficult, but not impossible.