There is a difference between signing the ROTC scholarship offer letter and signing an ROTC contract.
When offered a national scholarship, the letter you sign and send back to US Army Cadet Command indicating your acceptance and school choice isn't the "contract." If you get a Service Academy appointment after you have signed the ROTC scholarship acceptance letter . . . no harm no foul. You report in June to the SA, and the your AROTC scholarship is cancelled.
You sign the AROTC "contract" after you report to your civilian college/university (having passed the DoDMERB medical or gotten the waiver), and having passed the APFT.
You can then actually apply for a nomination to attend USMA via your AROTC unit:
http://www.usma.edu/admissions/sitepages/apply_nominations.aspx
"Applicants currently enrolled in an Army Junior or Senior Reserve Officer Training Corps (ROTC) program or an ROTC program from another branch of service that has been designated as an Honor Unit with Distinction are eligible for a nomination in this category. A request for a ROTC Nomination should be made through your Professor of Military Science or Senior Instructor who must fill out and submit a Request for
ROTC Nomination (Form 5-497) to the Director of Admissions, U.S. Military Academy."
So I don't think there is an issue with accepting a SA offer while on a ROTC contract. Have him check with his PMS if he is interested in pursuing.