VMI is a great school and would prepare him well if his goal is to commission to the AF, however I personally would not want to see my son go into huge debt to attend. Has he looked at what VMI can offer for financial aid? My son went to VMI and we were out of state. They offered a pretty generous financial aid package, then he received a 4 yr ROTC scholarship, so they pulled the aid. The ROTC scholarship made if affordable for my son and we were able to help him out with other costs not covered by the scholarship so he graduated debt free.
If your son feels the full ride state school offers the major and other opportunities he needs to be successful then I would advise going that route rather than going into debt to attend VMI.
If you and/or he can afford it and he does decide on VMI, make sure he knows what he is getting into. It's a great school but it is definitely not for everyone. My son thrived on the challenges there and has no regrets that he went to VMI, but it is definitely tough in many ways.
Good luck and feel free to PM with questions if I can help.