I got the email from "Roobet"
The email give me information about instant deposit bitcoin, did this feature will be no confirmation for the transaction of bitcoin.
I didn't receive any email from them. Maybe because I didn't make any deposit yet!
However, when you click on deposit you will see that 1 confirmation is still required:

You can get a problem if someone using "double spend" the transaction.
Not really, all they have to do is to disable withdrawals untill the deposit transaction has enough confirmations.
Can you explain honest how? Is your casino fully decentralized?
It doens't have to be decentralized to be honest.