The answer above is correct - he cannot activate the 4 year Type 7 at ERAU. He can use it/ convert it, and there are additional moneys the ERAU AFROTC unit may offer him to offset his first year costs. Very large AFROTC unit at ERAU. Very likely you already know, but the ROTC scholarships will not cover flight fees if he goes this path and those fees well, "ain't cheap".
My son is a private pilot also pursuing an Aeronautical Science with Flight degree - he too ultimately wants to be a commercial pilot. We did a lot of research and got boots on ground at a few of the programs last year. Know a lot about ERAU and can connect your son to an existing student if he has questions. Feel welcome to PM me if you or your son have questions about the various school flight programs or this path. Quick tip - is he starting to earn his PPL before arriving at school? could save you a lot of money if he does (but not additional / next certs beyond that).
Congrats and good luck!