I started off my freshman year running cross country at the jr. college level (believe it or not, it is the same time commitment as the top 4-year running programs). I also started AROTC right away in the fall (non-scholarship). My cadre told me I was required to come to lab, class, and as many PT sessions as possible. I ended up missing one practice a week (that I was required to make up), but I usually made it to about every PT session (3/week). I also drove about 30 minutes one way to get to the host school. So add all of that together and I had a lot of days where I would wake up before 4:30am and workout 2-3 times per day, plus I would have to stay up hours to complete my homework. I became so exhausted that my fitness level actually went backwards and I couldn't even compete at the national XC meet. Needless to say, it was way too much for a freshman. I decided to quit track over winter break in order to transfer to a closer university. Now I am training to run marathons on my own, and my PT score has actually gotten better (I have taken almost 2 minutes off of my run time) because I am not over-exhausting myself. I also just received my 3-year scholarship, which I probably wouldn't have been competitive enough to receive until I became fully committed to ROTC.
So I guess my advice would be, go ahead and try them both, but decide what is most important. Is his priority football or ROTC? He must realize that he might have to let one go in the end, it is way better to do that than spreading yourself too thin.