As I said in an earlier post (I think on this thread) I don't think it can ever hurt to call and ask. But I have to say, you knew you had APPLIED before the interview, right? It should have come up that you were also interested in USNA... and if they didn't ask you should have brought it up.
When I answered interview questions, I kept it general to becoming a military officer/attending a service academy rather than specifically an Army officer/USMA. I just mentioned that USMA was my first choice, but would definitely be honored to attend another service academy.