Question: Is it possible to be helped with therapy if you don't really talk much about your dp/dr?
Personally, I think so. In my experience, DP is a subset of anxiety, not a thing unto itself. What's ailing us is usually "cured" or "alleviated" not by discussing the symptoms, but by talking about our feelings about substantive, actual problems, situations, other feelings, especially our feelings about ourselves and our lives and the people in them, and so on.
Question: Because I have a really good therapist who's been helping me a lot with my anxiety and worrying but I get the feeling he doesn't really know much about derealization. Which I completely understand. It's pretty hard to know about it unless you've been through it first hand. So can I be cured without curing the dp/dr?
If he knows the basic outlines of the symptom, that is entirely enough.
If you have a sprained muscle in your leg, does your doctor sit with you and do the very things to the muscle that injured it in the first place -- over and over and over and over and over again? Or does your doctor send you home with the instructions to spend 30 minutes a day doing the activity that injured you in the first place?
Of course not.
In like manner, the immersing of oneself in the merry-go-round world that produces DP in order to have someone completely understand it is deleterious to recovery. For your therapist to understand DP, he would have to experience it, and I just know you don't want that.
If he knows it's a particular way of perceiving, if he does the minimum reading about the subject to get a general idea that it's a most uncomfortable state that its sufferers want to avoid, that's quite enough.
At bottom, his task is to help you create an interior environment in which you feel at home. Let him help you.