I see two and pay out of pocket. I have done so for almost 5 years. They do not know who the other is and I would never, ever, let them speak to each other about me. One is better at some things and the other has different areas where she is not unuseful. I did not ask permission and I would not let a therapist tell me whether I could see another one or not. If they had some policy against it, I simply would not tell them.
The first one just said it was my right to do it if I chose and the second didn't really say anything.