Their license only covers the comics. Anything that appeared in DC Comics they can do. Anything from other comic companies or from live action (tv shows or movies) they can't do. All characters Jim Lee brought with him from Image, into the DC Universe are possible. Same with Watchmen. Nothing in Marvel or [that stayed with] Image would be do-able though. Was Wildstorm brought into the DCU when Jim Lee joined DC? I think Wildstorm is still part of Image comics, isn't it? I don't remember the details on that. If it's not a DC Comics property it won't be possible. When Charon says that, I believe he means the CWverse versions of those characters specifically (since that's what was asked for) are not possible. They can still do Killer Frost, Flash, Vibe etc. because they're from the comics, they just can't do the CW's versions of them. He'll correct me if I'm wrong though.