I can see both sides of this situation.
It may give him a chance to recognize his triggers in the environment/relationship...go back and tweak his relapse prevention.
or
It may give him a weekend to go wild.
It's his choice regardless and will indicate how serious he is taking recovery.
I do have concerns that this wasn't something that they presented to you in private....prior to the "announcement." I kind of wonder what would have happened if your boundary was...."not until he completes rehab."