Chances are AOL is blocking the email if he's tried to have it send multiple times with no success. I would suggest having him try an address from a different provider (such as Gmail or Hotmail, if possible).
As a side note, the reason the main admin account has no control over other users' email validation is to prevent someone signing up under someone else's email address and then having that other person receive unsolicited email. The current validation system is set up in a way to ensure that the user at the registered address actually wants to receive emails from the forum.
