Having multiple accounts isn't allowed and even if he had requested support to close his first account, he should have confirmed from them that his account is closed and he has opened a new one or at least should have asked permission to open the 2nd account. These things may seem small initially, but they can create problems specially if you have high balance in your gambling account and suddenly you found that your account is frozen because you violate the terms and conditions. I think in this case, he should be fine if he has proofs of all those conversion with the support team.
Something even with support approval it still very adviseable to have them closed that account first, or better still make sure the balance on that account is cleared down to zero before you create and deposit into the newly created account.
The reason for this is that, why most casinos are against multiple accounts is that the gambler may likely make you of both of them to cheat the casino, so there is a likely system configuration that report two accounts that belong to same person and are active and one way to know an account is active is when there is activities on the Said account such as gaming or have deposits and withdrawals activities on them both.
If we can tell the reason why we want to close our first account and why we make another account, I think the casino may allow and will not do anything with our account. But if that is strict casinos, they will not allow that and will not accept our reason and still block or ban us. It is why we need to explain our condition and just hope they can understand the reason and allow us to make another account. But if they still prohibit, we don't have to against them because that can make us get another problem.