I think you were 100% right you didnt say no, just that you would talk to the
counselors(at his rehab) first.
My AH was in sales for along time ( addicts seem to have a special calling for talking people into things and make great salesmen)
and when he was in treatment he wanted to get a sales job and his counselors(at his rehab) told him NO, not for at least a year............said it was to much pressure and not enough accountability schedule wise and such.
I know its not easy but I believe that you did the right thing, and asking for a professionals imput is great that way its not just you, and the counselor can discuss the issue with your son further ..........
hang in there,