What matters is what the people who are considered 'experts' on the subject think. Magnus and Ahriman, the two characters in a position to know such things, both agree that there are no Gods. This is the metaphysics of the setting.
Lorgar and his Legion disagree. I suspect that the other Primarchs turned Demon Princes might have a take on it to
That said I think Voidhawk has the right of it and so will leave this here
All Comicshorse's posts come with the advisor : This is just my opinion any difficulties arising from implementing my ideas are your own problem