That's a really weird experience, it's the first time I read that. But what I don't understand is how did they know the deposit address was belonging to a gambling site? Usually one address is at least generated for each account. So they have no way to guess that fresh address belongs to a gambling site. For me the issue was not related to the nature of the business of the recipient.
I'm not sure if most gambling sites still does this but I know a couple of sites like cloudbet sends all of the deposits they receive in their hot wallet and there are others that wait for the transactions to accumulate before they consolidate it as a way to save fees.
I'm sorry but I don't fully understand what you mean. Even if Cloudbet sends deposits to a cold wallet or another hot wallet, it can only do this after the funds have been received. So when the user sends his funds from the exchange, the exchange doesn't know yet that the funds will be transferred later to a known wallet belonging to a casino. From the exchange point of view, the address looks like any common wallet address when the user makes a withdrawal to his gambling account.