CRO attains
DVC ressie availability through several channels. It is not uncommon to have cash availability but no point availability.
1) Disney/DVC retains some ownership (somewhere around 4%) for use as "maintenance rooms" as needed. If no major maintenance is scheduled, the rooms can be rented out though CRO.
2) DVC members who trade their points for cruises,
Disneyland, or other locations. DVC turns those points over to CRO to offset the cost of the trade.
3) Any room not reserved by DVC members on points are turned over to CRO for rental at 60 days out.
Occasionally, the 60 day points can be "recalled" by Member Services if needed. The other points (those owned by Disney and those used for trades) are removed from DVC inventory and can not be turned back over to DVC.
Also, in the case of resorts under construction (like SSR), any rooms completed but not yet declared part of DVC inventory (ie points have not been sold yet in that particular unit) are available to CRO for cash ressies.
But to answer the second part of your question...no, you can not make a cash ressie with CRO and turn that ressie into a point ressie for DVC.