Great job in looking ahead. The Summer Seminar application will require the submission of a personal statement, a 1,000 character essay. See the USNA website details for an explanation of what is asked for in the Summer Seminar application
https://www.usna.edu/Admissions/Programs/NASS.php#fndtn-panel1-Steps-For
From the USNA website:
If you have applied for our Summer Seminar program you do not need to submit a preliminary application, as they are the same application.
As USNA uses the Summer Seminar application as the "Preliminary Application" for prospective candidates then yes a personal statement will be
submitted as part of the Summer Seminar application. But for those candidates who submit a preliminary application after the Summer Seminar application window closes then the Preliminary Application used at that time does not require a personal statement.
See USNA website regarding the Preliminary Application
https://www.usna.edu/Admissions/Apply/index.php#fndtn-panel2-Steps-for
When looking at the Preliminary Application on the website the top of the page does contain a link to click for Instructions.
The Instructions do not specifically address the section titled "Remarks or Additional Comments" so I interpret that section to
simply be an additional section for comments regarding anything a prospective candidate may wish to explain.
I hope you find the above helpful.