Actually it is confirmed that he is in the game, just you probably cannot recruit him. I got the sense that since he is behind all the serial killing going on you could either confront/defeat him or avoid him or escape or whatever.
Upon reading this I was about to say "Oh, now that's clearly new information. First, where did we learn that ?" And before I could think much futher, I read
Agreed. You can’t recruit Durge as a companion, but there was a claim (I think in one of the Fextralife vids?) that someone (a dev?) had said that we might encounter them later in the game. I don’t think we know any more than that, but I guess it makes sense if it’s true that they’d be an antagonist of some sort.
Ok, so it's not completely clear yet. But let's assume, for now, that it is.
In that case, the Dark Urge is now : either a Backstory that you can apply to your Custom Character, or fully authored character you can meet in the game but not recruit (i.e. an non-Companion NPC).
Note : if you really want, you can replace "a mostly Custom Character, only with fixed Backstory" by "a somewhat Pre-authored Character, but the personality is not set, the "identity/visual" (name, sex, appearance, etc) is not set, and the game stats (Race, Skills, Abilitiy Scores, etc) are not set". It's just questionable, in terms of efficiency of the description.
But it's still not a Companion. Which means that, by Larian's definition of Origin Character, it's still not an Origin Character.
Anyway, now I'm more interested in the Dark Urge, since I will possibly get to meet them in the game. In which case, I presume it will be a male White Dragonborn, in terms of identity/visual.