Hello,
I am also going to attend Texas &M this Fall as Mechanical Engineering major. I have completed AP Calculus BC last year, and yes, my first reaction when I saw the requirement during my college research was same as yours. I took the MPE and passed with a 27 last week; it was a little confusing but the test won’t be so bad for a Calculus student. I highly recommend your son to do the practice test and go over the answers explanations. I would not have passed the test if I did not complete the practice problems. Oh, and you can’t really cheat; 1. Aggies don’t cheat. 2. Most problems are rearranging variables so calculator won’t help much. He will do just fine; there is no Calculus on there so don’t stress out 
Best of luck!