Sorry if this is off topic, but it seems the OP's question has already been answered, so…
That was pre Ward fluff too… When the Necron where cool anyways and working for the C'Tan.
Now they are lame. I doubt that the all the fluff about a big part of the mars priest secrelty workshipping the Dragon (a C'Tan) still stands.
Got to hate Matt Ward
Ward cannot actually override such an integral element of that canon at this point in time. The Horus Heresy is the most consistent of the "canonized" 40k lore, and Graham McNiell's HH novel, Mechanicum, is quite clear that fact the Void Dragon is, indeed, on Mars. Even if Ward is given free license to muck up the GK and Necron lore in the Codecis, his fluff does not override the concrete nature of the HH as canonical 40k lore. The Void Dragon is on Mars.
That being said, the nature of the Omnissiah is a complicated matter. According to Warp-logic, as described in the Liber Chaotica, there are actually 3, maybe 4 Omnissiahs.
Most gods start as nebulous "spirits," a vacuum of identity in the Warp that must be filled. People believe in them and feed them with the psychic effluvia that feeds them, until they are strong enough to have a limited effect on the material universe. They do this to build themselves up, until their worship makes them effectively immortal, their worship (theoretically) never ceasing. Once a warp entity can perpetuate their existence in this manner they qualify as gods. (The Chaos Gods do not fit this model, except for the perpetuation of self, so the appelation "god" still does fit, as the last is the only real qualifier. The Emperor is also a god, but in a different way)
The concept of the Omnissiah is immediately divisible into three distinct "individuals": 1) The Omnissiah as an aspect of the Emperor, 2) The Omnissiah as his own Warp individuality, the one worshipped by those who do not believe the Emperor and the Omnissiah are aspects of one being, and 3) The Void Dragon, as placed on Mars, as described in the HH novel, Mechanicum.
A fourth Omnissiah may exist, if one considers the Omnissiah worshipped by religious members of the Dark Mechanicus to be separate from the 2nd Omnissiah described above (Ex: the hereteks in Ben Counter's second GK novel, Dark Adeptus).
But yeah, the Void Dragon as Omnissiah is still a thing.
aha! Well thanx for that information, sir! So, the horus heresy novels are…..proving to be a disappointment…..Horus beat up by the Emprah's bodyguard, eh? Sad…..so much for Horus being a big bad……Dorn heresy's starting to sound more interesting…..it's always an arms race with wh40k, it seems - the next big thing is always better than what came before……
Constantine Valdor defeated Horus in a friendly duel in the early stages of the Great Crusade. The HH Novels don't seem to be going in the direction of the Seige of Terra anytime soon. The duel between them is not reflective of Horus at the time of the Seige, nor should it be taken as such.
so…wait…we're fighting about who won the 13th Black Crusade? Easy fix: it was a tie! Chaos got driven back, but they finally broke into Cadia…doubtless the Chaos stragglers will be hunted down (after causing much mayhem and misery), but Cadia will never be the same….the End Times indeed……
There has always been the presence of Chaos on Cadia. I would strongly recommend Aaron Dembski-Bowden's First Heretic. It's a wonderful read.