Hey sport, where are you getting your intel?
Moore used John Constantine as a guest character in the Swamp Thing series. When Constantine got his own comic, Hellblazer, Moore was not part of it, nor has he been for the last 220 issues or so. It hasn't been "his" character for a long, long time.
Furthermore, the story goes that Moore came up with J.C. only because the Swamp Thing artists wanted to draw some guy that looked like Sting...I doubt he has ANY emotional ties to the character.
League was done for Dark Horse Comics, so how DC could possibly screw him on this is beyond me...