WOW, i first saw this post about a month ago and have read everything in it..
i have a brother who is not really OTD but is very rebellious and will do anything the opposite of what my parents tell him. i am not saying that he is OTD b/c he still does mitzvos but he does many things that are not in line with our schools/families tenets.
I dont know your son, but from experience with my brother, i would say not to mention anything to him aboout the shlichim that have connected with him unless he mentions it first. He probably does not want you to know about that part of his life yet.
I always daven for people like my brother and your son. I feel like that is the best way we can help them.