What does the application say? I have read posts that say the POE cannot be from a coach. But I think a JROTC instructor is allowed do it (not 100% sure) and I know the JROTC instructor is allowed to administer the CFA for USNA (because the USNA web site says so.) In my state, JROTC exempts you from PE too, and the JROTC instructors are full time faculty members and retired senior NCO's and a retired commissioned officer, so I am almost positive they can do PE POE's
Not sure about JROTC instructor, but it seems reasonable if the instructor observes you in physical training - ask RC. When in doubt, contact your RC. They can approve a substitute for a PE instructor.
Acceptable substitutes in the past have been anyone in a position to evaluate your physical skills, except for a team coach: martial arts instructor, dance instructor, etc.