Aside from Ulric, I think the Kislevite gods, Daz or whatever (I forget the names, if anyone else could help there) plus 'Olric' and the other Norse gods we never see (assuming they're not all redundant now in favour of chaos) are the most primeval, 'realistic' seeming faiths in the Ol' World, and that's where the creation myths would probably survive. In the progressive, 'civilised' Empire down south there doesn't seem to be one.
From what I understand, the Old Ones stuff is not common knowledge for humans.