I'm unclear on what the goal is. I think you/he are jumping the gun. midyear starts at all but the largest of universities are inviting hassle and weirdness. Trying to enter midyear seems forced.
ROTC wise: NSI/NSO will be a significant bonding event for a new class. Also, I will note all the schools my son applied had annual openings for college programmers in the May/June timeframe. They were at least reported competitive process (ie. looking for young people who can convert to scholarship or AS). Lastly, I'm not military, but I've learned enough in a year that the military doesn't like exceptions.
Academically: Calc, Physics, Chem, etc all follow a pattern by semester or quarter. That pattern is set up for Fall freshmen. Buyer beware trying to program for a Spring entrance to a tech major. You will find replacement instructors teaching the retreads from fall who are repeating the course, potential class availability limits, weird breaks in the sequence ("Wait, what about the Fibonacci sequences from before summer?"), all the cool kids already in a study group.
Can you tell I highly recommend a local JC/CC where he can knock out Speach, Criminology, Art history, Writing, Music, foreign language? And knock off GE requirements at low dollar costs.
His time better is served to research what transfers from JC/CC and plot that strategy. He can also actually look at the major requirements and roadmaps many schools have to figure out the slack AP/CLEP/JC/CC course would provide. By day one of fall, he should have the course plan his MOI is going to request.
Or work, or hang out with that girlfriend you don't like, grow his hair out, start a window-washing business, get swole, eat mom's cooking.
If he is considering reapplying in the fall as a national candidate, just measure the number of units and keep under 30.