You can always ask for advice (traits of successful students, etc). People love to talk about themselves/their careers.
I also think the "what would you change" is a good question. Most physicians won't just lie through their teeth, even to make their school look good.
Also, make sure to ask student interviewers about positives and negatives. I can't just come out and spill the tea about my school, but I'll tell you the truth if you ask about retention and board failure rates for example........