Okay, so I went ahead and read it just now.
"In short, it can be said that one must sometimes deplore the unjustified intrusion of the psychologist in the depths of the personality and the serious psychic harm resulting therefrom to the patient and even to third parties. "
The main theme in regards to accessing the subconscious or hidden psychology of a person revolves around consent and the right to expose secrests. A person can give consent on his/her own behalf. So, methods where a person has the ability to reveal truths about him/herself with their own consent are moral. However, hyopnosis devles in to the subconscious during a semi-conscious state, and a person in a hypnotic state does not have to ability to choose what to reveal or not reveal. Therefore, they are in a position where they can reveal secrets of a third party, which is prohibited. Therefore, hypnotism would be immoral.
Anyway, those are ust my thoughts after reading that document by Pope Pius XII. If you want a more-true answer, you should probably ask a Priest. :thumbsup: