I've had two of my professors recommend that I ask questions as though I were an admitted student. Specifically, one of them mentioned that I should think about the things I'd want to know in order to choose between program X and my other options - especially if I got a last minute offer on April 15th. Given the unpredictability of waitlists this could very well happen, so it's good to be prepared for that in advance! (And, if you need to decline, it's a courtesy to others on the same list).
I definitely feel this pressure too though.