Most of this inventory comes from
DVC Members using their points to trade out for
DCL, ABD, or the Disney Collection. Those points are used to book rooms that are, in turn, rented out to the general public at "market rates", and the revenue received (less a cut to CRO for marketing) is used to pay for the cruise, guided tour, or hotel stay the Member chose.
The general public, when renting hotel rooms or villas, expects daily housekeeping, so it is provided. I suspect there is some mechanism to also recapture some revenue to pay for the higher housekeeping costs---either via the $95 fee, or some other reimbursement from CRO to DVCMC.
Disney also owns points at each resort---some for maintenance intervals (which I'm guessing they do not rent except as breakage) and some from foreclosures, etc. The points Disney owns via foreclosure are theirs to do with as they wish, including rental. I suspect that there is also a mechanism here to recapture those extra costs in some way. You would have to inspect the budget to be sure. I would guess that there is a negotiated rate at which CRO pays DVCMC for these services, but probably not quite the same level that a Member pays for additional cleans.
As for whether or not the accounting is done properly: you have two choices. You can assume that Disney is playing by the rules, or you can be skeptical and live with never knowing for sure. If they are trying to hide some improper transfer payments, you will probably never discover it without having direct access to the accounting data and a *lot* of time and auditor manpower. After all, DVCMC is audited annually, and *those* folks don't find anything improper. What are the chances you will if you go to the Orlando offices and ask to see the books?