Key words here are "volunteer swim instructor." Sounds like extracurricular volunteer hours, not observation hours. You can check with individual schools but I put money on them not allowing it since you're not observing anything related to PT directly. From everything I've seen here, PTCAS requires observation hours to be "signed off" by a licensed physical therapist. So if one is there, you might be able to have them sign off on the hours. But if you get into an interview and they ask about it and find out it's not actual observation hours, itll look like youre lying/fidgeting hours and hurt your chances.