Frankly, if his religion impacts his ability to be a therapist or doctor he is in the wrong profession and he may be breaking the law. Many areas frown upon this (ie. a pharmacist is not allowed to deny a morning after pill regardless of his/her religion).

I have recently been arguing with others over the question of how much to tell. I am a hardliner when it comes to this believing pretty strongly that you tell everything. In my opinion it serves you no purpose to keep things silent from your mentalhealthcare worker. The goal is to get healthier and that isn't going to happen without honesty.