I'm waitlisted at BU, and they've been extremely helpful in answering all of my questions. I've had several conversations with the DGS, my POI, and current grad students. I also asked permission to sit in on a graduate seminar to see what it was like, and everyone involved was very nice about that, too. I would definitely encourage fellow waitlisters to reach out to anyone who might be able to answer your questions. BU actually invited waitlisters to their open house, so they might be more accommodating than other programs, but I think you certainly have the right to put your questions out there.