RCI has been taking a lot of the DVC inventory and renting the reservations
If you look carefully, you will notice that the rental inventory is actually through WDTC, not Member Services---you use WDTC's web site to arrange for Magical Express on rentals, but call Member Services to do so for exchanges.
Member-owned and Disney-controlled inventory are managed completely separately with DVC resorts. So, in this case at least, RCI isn't renting out member deposits, but acting as a rental outlet for WDTC for breakage inventory (the RD## codes) and, I suspect, inventory that Members have used for "internal" exchanges to
DCL, the Disney Collection, etc. (the DV## codes).
The DV## rental pricing is usually only a bit better than rack, but the RD## prices can often be decent. Plus, RCI will act as a front for most of the promotions Disney is offering on DVC inventory, but you have to call, and there's usually no real advantage. Every once in a while RCI members will get a slightly sweeter deal---they recently got buy 3-get 7 during the period when Disney was offering buy 4-get 7, for instance.