HPSP Army Scholarship?

I am a high school student looking at becoming a physician. The army offers the HPSP scholarship that, from what I can see, pays for medical school in exchange for X amount of years of service in the army (depends on how many years you get the scholarship for). My question is this: do you have to go the ROTC route in undergrad to be considered for this scholarship? If so, would you be able to complete undergrad and med school before being on active duty?