"Erm, what part of Moore's work is crucial to Blackest Night?"
There was an eight-page back-up that Moore did (I think it's called "Tyger Tyger") which introduced the 666 sector, with all it's survivors cruxified, and the prophesies that Sir would start believing--including the Blackest Night.
So the basic idea of it happening does come from Moore, though Johns did add a lot of his own ideas into it--which kinda makes Moore full of shit here.