The PAL one does for sure, so I'd say the US one too. However, since this RGB signal is supposed to be used through scart, I think the sync gets mixed with the composite signal in the same pin, which makes it not possible to use in some RGB monitors. This can be solved by hacking a VGA box.
Too bad there's not a whole lot of room left over in a Dreamcast, because it would be great to just slap a VGA d-sub connector on it and use a VGA extension cable to hook it up to the monitor. There might actually be a bit of room to do this; I will have to do some more investigating and find out. Cool stuff.