CRO gets DVC rooms in several ways.
Disney retains a small portion of ownership (estimated at 4%). These rooms are used for maintenance, but if they are not needed for that, they are available through CRO.
Whenever a DVC member trades to a regular Disney resort,
Adventures by Disney, Concierge Collection, WDW resort or for a
DIsney cruise, rooms are made available to CRO, to help offset the cost of the trade.
Any rooms unreserved by DVC Members at 60 days out are turned over to CRO, proceedes from this is called "Breakage" and ius used partly to offset our dues.
So overall, someone has a pretty good chance of booking a DVC room for cash through CRO. And in fact, there is often CRO inventory available when there is not point inventory available to members.