The quality of counseling is going to depend a lot on the counselor. If s/he can't separate their own biases or has a strict "it's always the mother's fault" attitude, you're not going to have good results. On the other hand, counseling won't be like a nice tea party. Ugly issues and attitudes may come out. Honesty is sooooo important. But you can be honest and polite at the same time, contrary to popular belief.
If your son insists on picking out the counselor, do some research on whomever he picks.
Counseling is just a tool. You can have the most tremendous sessions ever, but if no one changes actions or attitudes the other 167 hours a week, the relationship won't be healed. An alcoholic can attend 3 AA meeting every day, but if s/he continues to down a bottle of wine a day, no recovery will happen. I've known some instances where people complain about the time they spend in counseling but nothing seems to get better, but on closer questioning, you realize they aren't doing anything but attending their sessions.
Also, it's easy to blame the counselor if results aren't forthcoming. Sometimes it is the counselor's fault - at least partially. But you need a lot of self-honesty to make it work. Not everyone is up for that.