My understanding is that you will only be subsidized for a degree at RMC (or at a Civvie U via ROTP) if you do not hold a degree that fulfills the requirements for the trade for which you have been selected. Thus someone with a Nursing degree who wants to be an Engineering Officer would be able to get an engineering degree at RMC, someone with an engineering degree who wants to be a Nursing Officer would be able to get a nursing degree at a civvie U (since RMC doesn't do nursing degrees), but to get in under the ROTP you would need to be applying for a trade which has actual requirements that you don't meet.
There's a matrix out there that lists various types of degrees and various trades, annotating whether or not (for ROTP) they are "preferred" "fully acceptable" "acceptable" or "not subsidized". If you already have a degree, in order to be eligible for ROTP entry into a particular trade, the degree you already have would have to be, by my understanding, listed as "not subsidized". Unfortunately, the copy of the table that I've been able to find online was scanned in with absolutely terrible quality, so it's kinda hard to read. I might be able to help you figure out if your degree would be considered acceptable for the trade you want if you let me know which trade it is you're looking for, or your recruiting centre should have an actually legible copy of the table (in Annex A of CFAO 9-12 Regular Officer Training Plan)
That having been said, for siuto, I think you may be out of luck with the plan to take a 2nd criminology degree, as as far as I can tell, there are no trades which consider a criminology degree to be acceptable that don't consider a "languages" degree to be acceptable. With a linguistics degree (let alone the MA) you're alredy considered better suited academically for every trade that would accept a criminology degree other than the security grouping (I think Military Police Officer might be the only trade in this branch), which ranks criminology as a "preferred" degree and languages as a "fully acceptable" degree.
For Trick, when you said that if you stick on civvie street that you'd probably continue on in medical research. Is it safe to say that your BSc is in biology / biochemistry? If so, that degree would not be acceptable for EngO (or CELE, EME, MSEO, NCSEO, AERE), and you should remain eligible for entry under ROTP to those trades.