Normally Admissions asks for documentation or validation of the activity. They might take your DS's word or might reject and ask for validation from a school official or the adult overseeing the actual project.
I am not sure how Admissions would look at this addition, but likely as just another activity, as your DS hasn't DEMONSTRATED leadership in that position YET. In other words, if the question was asked..."so what did you do as chairman of this project?" There would be no answer. Apparently USNA will add these activities into the record, but I am (and my opinion doesn't count, thus I recommend you move forward) not a fan of activities that candidates WILL DO...as they HAVEN'T DONE it yet. In my mind, there are too many variables that could change once the activity happens (i.e. predicted roles/responsibilities change, grades slip, etc.).
Best of luck to your DS on the project. Definitely not saying your DS won't come through, but making the statement as a generalization.