I would think with the increasing occurance of food allergies (not to mention possible religious dietary restrictions), it is not fair to judge someone for not eating your food. The polite interviewee is probably not going to say, "I'm allergic to nuts" or "I'm Hindu and only eat strictly vegan"(and since they don't know how the food was prepared, they can't know if its OK for them to eat or not (even if it looks OK), they will probably just say "thank you, but I'm not hungry." Really, what someone eats for nutrition, really has no bearing on their ability to do the job (at least in pharmacy, not like you are hiring someone to taste food for quality control or something.) Although I do think it is nice of you to offer your interviewees food, only once on a hospital interview was I offered food, and I was taken to the cafeteria where I could choose whatever I wanted (and they had quite a varied choice, so that seems to be a better way to do it, then the person can order whatever they need)
Back to the OP, for staff hospital interviews, I have never been asked specific clinical questions, only about my experience in dealing with certain things (like, "how much experience have you had with aminoglycoside dosing?") If you are licensed, most directors are going to assume you have the requisite knowledge, they are going to be more interested in your experience in applying that knowledge.