It's on a treadmill and at a zero degree incline. That's what it states in my blue info book sent to me the other month for my own date at the OASC. Not the hardest of physical tests I agree but at the end of the day you go to the OASC to show your potential.
You'll not start sweating blood and tears until the actual course and that's if you get through. I am aware that on the first day of NCAITC all students must complete the 1.5mile run outside in the same time as decreed by the required standards for their age and sex.