I know I read somewhere that the 7th semester transcript is required, but I think that was for USMA, as people are now receiving emails requesting it. I do not think that USNA asks for it anywhere, but we went ahead and sent it in anyway, especially as it may be in the fine print of instructions somewhere, as USMA's is.
The USNA Certificate of Acceptance/Declination does state that:
"I understand that this appointment may be withdrawn because of failure to maintain satisfactory academic, moral or conduct standards, or because of a change in my medical status."
I guess your transcript is the only way for the academy to measure if your academics are remaining satisfactory?