All MOCs have access to see if you obtained a nom from another source. The MOC staffer may, or may not, choose to look it up prior to the interview and may, or may not, choose to tell the nominating committee about it.
I have seen candidates in your situation asked in an interview if they have received other noms. Always reply truthfully - failure to do so may cause the panel to question integrity (I am not implying that you would mislead them - I just stress the importance of understanding the situation). I recall a time when a candidate had other noms and when specifically asked if he had applied to other sources for a nom or if he had received any noms he tried to imply that no such nom had been received. He had to do some very significant back peddling when called on it by the panel (which was made aware of the other noms). The discussion between the panel when he left the room was almost fully about integrity. Honesty is always the best policy.
Again, I am not implying that you would do otherwise, but am reminding you and all other candidates that the MOC staffer has access to significant information and may choose to relay anything to the panel.
If USNA is your first choice, and you have a USNA nom and LOA, your panel may ask you to discuss your first choice SA (the staffer CERTAINLY knows you have an LOA - the panel may be made aware of it as well - but not all MOC's give that info to panels). Although you may not know who is on your panel - rest assured ALO's, BGOs and MALOs are in contact the MOC's. This time of year the MOC staffer responsible for nominations is talking to these people, as well as the actual SA's, every single day. If you have told your BGO that USNA is your 1st choice - you can bet the MOC will have been made aware of that fact. Granted, not all BGO's/ALO's/MALO's are in close contact with MOCs but the possibility exists and you should be aware of it.