And DC maintains that Vulcan and Lightning are the same character.
I still don't think of them as the same character. I think of them as two different heroes with similar powers.
Well, that was the company line. For years when people would ask about bringing the SF characters into the DCU, DC would say Black Vulcan was already there as Black Lightning.
Along those lines, Joe Kelly -- scribe of last JLA series 61-89 or so -- told me in person at WWE 2003 that his creation Manitou Raven was a tribute to and an attempt to get Apache Chief into the DCU and the JLA as well. Kelly said he thought of Apache Chief as someone who had been on the team for a long time, but was just always off panel, never getting any screen time. So he put him in the JLA.
The Wonder Twins appeared in both Extreme Justice and Young Justice.
Maybe these days the SF have one of the 52 worlds to themselves?