A good psychiatrist can almost certainly use knowledge of a patient to interpret dreams of that patient assuming the patient remembers and reports accurately those dreams. I have done that a couple of times (kind of showing off/fing around) and in both cases the persons agreed my interpretation made a lot of sense to them. It helped a lot that I knew about the situations that they were undergoing at each of the times.
What Fritz Perls did in his therapy wasn't dream interpretation. By having clients role-play everything in their dream, and have conversations with the things in a dream, whether animate or inanimate, and having the client role-play dialogs between the things in their dream, the clients would gradually create the (emotional) meaning of their dream for themselves. No woo involved. And certainly no third-party "interpretation." Perls often referred to dreams as "unfinished business" -- the unfinished business of the client's life, not anyone else's. The role-playing served as a way for the client to externalize the feelings represented by the imagery of their dream.
IMO the very thought of someone "interpreting" a dream for someone else smacks of pure woo.
M.