Buddhism is a psychologically astute practice. It invites deep scrutiny of the vicissitudes of the ego-driven self, it acknowledges the strength of the forces that push and pull us, and it is not at all polyannish about the prospects for overcoming the defilements any time soon. It is no surprise that many have found some common ground between Buddhism and this, that or the other psychological theory.
Still, practice is not therapy, being a teacher is not the same as being a therapist, and insight isn't something like maintaining mental health.
I've begun to wonder if there isn't a "near enemy" issue between the two, particularly when a) the teacher is a trained therapist and b) the student is in need of psychological/psychiatric counseling. How hard it must be in those cases to keep things straight! If the teacher is an electrician, it's a lot easier to keep one's day job out of the dokusan room or off the teisho tan. If the teacher is an algebra instructor, there might be some issue of treating the assembled sangha like a class of students, but at least there won't be content confusion. From the other side, if the student is not needing counseling, then one can be just that much more sure that one is really seeking spiritual direction and not just a free session.
Maybe I'm making much ado about nothing.
Still, I've heard far too many teishos with a 10:1 psychological theory to Dharma ratio, and I've watched people get all twisted up in the psychology of their practice rather than just dealing with it as practice. I know a couple of people who do Zen as a kind of self-help exercise along with their acupuncture, men's group weekends and empowerment classes. In none of these cases is the admixture of psychology and the Dharma a good thing.