Probably the more correct way to say it is the standards are the same (officer and enlisted accessions are based on DODI 6130.03) BUT are
applied differently.
It's a separate philosophical discussion on the ethics of applying the standards differently based on whether you want to become an officer or enlist. Some people don't think it's right. Others might say the 2 populations are different so the standards have to be applied differently to reflect the different motivations, abilities, goals, etc... But I digress... again, that's a whole different conversation.
Allow me to pretend I'm part of the current WH administration so I can walk back (or clarify) my original statement.
Can anyone choose DODMERB or MEPS? There is no directive, law, policy, etc that I am aware of that says SA or ROTC applicants shall go to DODMERB and those who want to enlist shall go to the MEPS. However, if someone goes to a MEPS and says I want a DODMERB exam, that person may be told something along the lines of, "Huh? We don't know how to do one of those. We do MEPS exams. Here's a urine cup. Please give us 30cc of urine."
If someone wants to enlist and tells the recruiter he/she wants to go to DODMERB for the exam, the recruiter is going to say, "What's DODMERB? I'm taking you to the MEPS. Sign here."
So let's say someone wants to go to ROTC or SA and gets to the MEPS. The MEPS does the exam. The MEPS will submit the exam to the DODMERB reviewers for disposition. So, the exam will be done at the MEPS BUT the disposition will still be done at DODMERB. Normally, the MEPS doctor will decide qualified/not qualified at his/her level for enlisted. For ROTC and SA, the qualified/disqualified decision is centralized at DODMERB. If you want to go to the SA or ROTC, there's no way of getting past the DODMERB reviewers. The physical exam will still be dispositioned at DODMERB if MEPS does it or a DODMERB contract doc does it.
If I were advising kids, I'd say go to DODMERB if you want to go to the SA or ROTC. Go to MEPS if you want to enlist. I'd give that advice even if a choice were given.
Full disclosure... the MEPS exam is more rigorous than a DODMERB exam in most ways. For example, you will give a urine sample to check for protein and glucose at the MEPS. You won't give a urine sample if you go to a DODMERB doc. There are lots of false positive with using urine as a screening tool for diabetes and kidney problems in a population with low prevalence of the disease. Heck, if you do vigorous exercise the day of or day prior to giving a urine sample, you may spill protein. If you're positive for protein or glucose, then guess what? You'll have to chase it with your primary care doc. With a DODMERB exam, you don't have to give urine. In medicine, they say if you don't want to find it, then don't look for it. The MEPS will look. DODMERB doesn't look.