If he is indeed a real Doctor, then yes, it is an ethics violation and he could lose his license- unless Twitney was dumb enough to sign some release.
Even if she did sign a release, there may be a case to say she wasn’t in her right mind at the time she signed it (ie he took advantage of her when she was mentally unstable).
Dr. Phil, have the ratings gone into the toilet that badly? How’s that been working for you?