As for their hot wallets and client deposit addresses, these are a bit more tricky because not every one of them is tagged as being a Huobi address.
Most of the exchanges never hold any of the customer's funds in hot wallets and the funds we send gets transferred to cold wallets immediately. Apart from that, the wallets generate random addresses through getnewaddress command.
The buying and selling of coins in an exchange takes place only in the front end of the exchange. You won't be seeing any blockchain transactions taking place. This is why if a cold wallet gets hacked, the total funds are transferred and the exchange results in a loss. The coins are never held in the users account. Hacks in a centralized exchange are more riskier and this would result in complete loss of user's funds.
This is the reason why coin selection algorithm and database maintenance plays a significant role in centralized exchanges and I hate holding funds for a longer time in centralized exchanges.