if your therapist has made you aware, or given you the impression, that they are adamantly against ANYTHING, that is not a good therapist and you are not safe around them. that is not at all the purpose of these services and i would strongly warn you against proceeding with this person any further.
as far as hypnotists go, there is no reason they should ever be asking for such a letter, nor would any reputable professional recommend such a service. hypnotism is not considered a medical practice, nor are there any risks associated with it which would ever require another's recommendation. i think this hypnotist is...probably messing with you.