Medicine and medical education is a large and long-term time commitment, in or out of the military. You can teach in medicine, but that comes after first going to medical school and residency and probably fellowship. As far as practicing medicine in the military, in a general sense, that is what the military will expect you to do, and not something else. Some find opportunities to work in medical research or administration, but those come after first completing residency training after medical school.
A teaching certificate as a secondary school teacher has no relationship to medical education or teaching in medicine. That is a fundamentally different career.
ROTC doesn't exclude the possibility of your going to medical school, but you should understand the main purpose for ROTC from the military's point of view, is to produce line officers, not doctors. Its demands may delay your being able to complete medical school prerequisites, which can be an obstacle. ROTC also doesn't exclude your becoming a teacher someday, but it is a program meant to direct you toward a military officer career, not an educational professional career.
USUHS and HPSP have military entrance physical requirements that must be met, similar to ROTC.
Becoming a competitive med school applicant takes a lot of work and time, and requires a mindset committed to that goal. Getting other qualifications, in teaching, law, business or engineering, for example, are possible, but eventually you will have to prioritize one over the other, and certainly if you are serious about medicine.
