I'm pretty sure that's just NiGHTS... at very least I wouldn't say it "is clearly not NiGHTS." It does look a little different, but I think that's to convey that the character's dark past.
I'm under the impression that Selph was never fully designed. But I'm probably not the most knowledgeable person... does anyone know otherwise?
I actually thought that when I originally saw the picture. Then I realized that it was all the boss characters and thought, "NiGHTS isn't a boss." Of course it could just be all the 1st and 2nd level Nightmarens, but with NiGHTS already in the picture he seems redundant.
My understanding is no one knows if anything was designed for Selph. We know something was "deleted", but we don't know what. I'd find it hard to believe they would not have had any designs at all for a character that was going to be a main boss and that they apparently had enough stuff programed in to have to delete it.
Either way though, if it is a picture of NiGHTS before he rebelled, then it's the only picture I've ever seen of that either. So it's a pretty important picture (imo) regardless.