SCART is simply a connector format. It doesn’t define the actual signal. The (shitty) connector can carry composite, s-video, RGB, component, audio, a switch signal, etc often several at the same time.
It will almost never carry RGB from a VCR/LD/DVD player because VCRs and LD were native composite and the number of players ever produced that could transcode to RGB could be counted on one hand. Fully legal consumer DVD players rarely if ever output RGB because it doesn’t support Macrovision which was a required part of the spec.