Are you aware of any RN's on a medical school faculty? As far as my own school, I've been there for 4 years and never met one.
If the situation is, as you presume, an RN/PhD doing research and on the faculty, then maybe it is appropriate. Maybe.
But I really think you're over-generalizing the purpose of the med school interview. The purpose is to determine what kind of person you are, how you handle stress, and how you will fit in in medical school. Nurses, even faculty nurses, have only a passing understanding of the medical education process, and have never experienced the rigors of medical school.
When you consider how much of medical education occurs outside the classroom (clinicals, endless studying, independent research, etc), even a nurse who is faculty will only know what he has heard, since he has never and will never experience it. It is really no different than having a research assistant, department secretary, or hospital tech conduct the interviews.