Rehabilitation of cheaters.

Should I reveal his current nickname?

It's not worth revealing his nickname to everyone, since this player hasn't been caught cheating on HeroesWorld yet, and ruining his reputation prematurely would be wasteful towards him, IMHO. But Pete and other forum members who have weight on HeroesWorld and play often should be informed. After all, the saves need to be checked if there were suspicions...
P.S. I wouldn't mind knowing the nickname, but in a PM. :)