I've never seen a VCR that outputs RGB. I guess it's possible that some of the teletext-equipped model did, but certainly I can't see the sense of having a complete PAL decoder in a VCR. S-video is as advanced as I'd expect to see from a VCR.
The later DVD or HDD recorders mostly had RGB inputs because they were capable of recording in much higher quality than VHS. As you say, they made handy HDMI converters