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.
I guess he will never get an approval to create new account if the user still have an access to his old account. So lets assume that he totally lose his access to his account in this casino since he maybe lose his email. Then ask for approval towards creating new account since he still want to play then get approve by their support.
With that situation I think we don't have anything to worry especially if the support already approve and take not about the situation.
Provably users in that situations won't encounter any multi account issue.