I believe (please correct me if I am wrong) that the application for the Citadel already closed back in July for the class of 2013. I know that they are already sending out academic acceptance letters. VMI's application doesn't open until September 1st.
The Citadel and VMI both practice rolling admissions- The Citadel's has definitely not closed already for the class of 2013 (although I can't find a published date for their decision points). VMI's deadline for Early Admission is Nov 15th and for all applicants is Feb 1st.
Good question about getting your interview for ROTC scholarship. For Army ROTC - Cadet Command will help you set up an interview at the nearest ROTC detachment. However, if you can do so, once you complete your application- I personally would suggest that you try to arrange your interview with the detachment that is your primary choice. Although it appears that the Army has centralized the decision process more this year than in years past, I am certain that the PMS at each school will still carry some weight in the decision, so interviewing there if you can do so would seem to be a plus. Additionally- it will give you a clearer picture of life at that school. Balanced against that of course is the cost and time involved to get to your first choice school.
At the end of the day - regardless of where you are interviewed, make sure that you spend a fair amount of time preparing yourself for your interview- with a lot of practice interviews in front of people who will give you honest and constructive feedback about your answers, your reasoning and even simple things like your manorisms. All of those things are important in creating a solid impression on the person interviewing you.