JR pass eligibility

Hello! I am planning a trip with my boyfriend to Japan. He is a part of the U.S Air Force and will be coming by military plane into a military base. However, he will be here only for tourism and is currently stationed in South Korea and has time off work. Is he eligible for the JR Pass? He will have the paperwork proving that he will not be here for more than 90 days (the longest he will stay is 20 days or less). Or does he strictly need to arrive through commercial airline? Thank you!