Before I post some points about the topic I want to keep it as a simple question and let others weigh in first. With the addition of 2 other spirit cards, should grey Wraith gain the undead subtype to match his ghostly brothers or is he fine where he is as the only dark nonliving creature who isnt undead?
Should it be? Other than saying that it doesn't matter because it won't get changed... I'd offer my opinion that it probably should. Personally, I don't get how a Ravenous Ghoul should be Undead and the Grey Wraith should not be... especially as other Spirits also are Undead, as you note.
I am fine with other Dark Creatures not being Living while not being Undead... I could imagine a few anyway... but this is just one of those wonderful things that makes the game feel disjointed to me.
I'm not sure where you are going with this, but you should get used to it. There is not going to be any official change.