I believe you have been misguided as well; I was able to complete my medical evaluation long before the completion of my application. In fact, I got it done as soon as I finished my candidate kit and received the dodmets package in the mail.
As for the WEST POINT INTERVIEW, not the nomination interview, I am not sure whether that is mandatory or not, but from what I've read from the posts above, perhaps they are optional. When I sent in my nomination applications, I received a form letter from one of my senators advising me to schedule an interview with the academy. I promptly emailed my regional liaison, and he was happy to find an admissions office worker near my location to meet with me.
It should be noted, however, that when I was at the interview, my interviewer began by reading me some legal codes and explained to me that the Academy, as a federal institution, had the right to interview me, regardless of whether I wanted an interview. I wasn't sure what to make of that since I had personally schedule the interview, but there you have it.