Sort of. Unlike most schools, where class size is set at a desirable number but the school can typically handle more in a pinch, USNA's admissions numbers are set by the government and they can't go over that. So, even if they see more people declining than anticipated, they are unlikely to take folks off the WL until the number of possible acceptances is less than the desired number of plebes.
So, if the magic number is 1132, and they have 1100 acceptances but 40 offers still outstanding, they're not likely to take anyone from the WL. If they have 1100 acceptances and only 25 offers still outstanding, they could start looking at the WL. Generally, however, they wait until the deadline for accepting offers of appointment has passed (May 1) before considering the WL. Also, there are folks with conditional appointments who are awaiting medical clearance, so some WL folks may not hear anything until quite late.