Yes John Matthew is Darius, JR Ward says so right from the beginning when Rhage's book came out. It is why John is mute, because it was the bargain that Darius made with the SV when he chose to be reincarnated. She would take away his ability to speak and all memories of Beth. So he had a seizure when he first met her, but he doesn't remember her or know why he passed out. I think that once he has his transition he might get all of Darius' memories as well.
