When my ex was in rehab a counselor called me. He told me that he was concerned because my ex said he wasn't really an addict and that he was only there to get me off his back. The counselor, of course, saw right through that, and wasn't at all surprised when I explained to him how serious things really were. After that he called me a few times to let me know that ex was finally opening up and sharing, and that he could see he was making progress.
So I think it can be good to involve family members.