The "Roger Williams" did have third-rail pickups, that I believe drove a GE traction motor for when the trainset was running into GCT in its intended role. Unfortunately, the Roger's third-rail systems were as buggy as the rest of the other McGinnis lightiweights.This equipment was removed when the Roger was downgraded and put into commuter service.
However, the Roger Williams equipment were not RDCs, but a combination of RDC components with lightweight coach shells. If you take a close look at the posted photo, you'll note they are slightly different in size than the standard RDC that they're coupled to.I believe this was done to allow them to operate within the tighter clearances of GCT. In fact, IIRC, the Roger's radiators were original slated to be mounted in the sides of the units , thus freeling the roofline for domes, hence the requirement they be as compact as possible. When this idea was scrapped, the radiators where instead located back to the traditional, albeit lower profiled, RDC roof blisters.
(P.S. theres also one of the cabless "B' unit Roger Williams coaches in the process of being restored for use as well, IIRC...)