I guess that is fine. I did my previous study in Europe, which has a bit more hierarchy. However, from what I've gathered people in the US are more flexible, and its fine to ask for more information on the interview. I would also like to know what to prepare for. Sometimes, its a very specialized interview - where Professors ask in-depth questions about the project. Sometimes, its very bland (Why this school? Why a PhD? What are your plans?), and sometimes there can be outside specialists asking you about Art History in general, books you've read.
In all cases, it takes a bit time to think about all of it - so it might not be bad to have more information.
Any idea how their shortlist/decision making works?