Yes, they can violate him for that. He could also be violated for the disorderly conduct. No, he can't appeal it until he is convicted and I'm not sure what the appeals process is, if there is one, for appealing a violation of probation. He is free to fight the violation but it will be an uphill battle. It's way too late to appeal a 10 year old conviction as far as I know. Did he not have legal counsel? His parents should have been involved even if he was removed from the home.

