If you mean RGB SCART, some consoles are modifiable to output RGB but not all. I think the Genesis is. The NES is not without stealing some parts from a Playchoice. Google usually knows if a given console has a simple mod.
If you just mean "something I can hook up to a SCART intput on a TV", SCART supports composite video. Pretty much all consoles since the NES have had composite video output options. Placing this on a SCART cable isn't hard, but it won't work with an arcade monitor.