Interesting, but that kinda goes against what the base-story is. The cult wouldn't need to resurrect Dracula since Simon is already poised to do that. If anything the cultists keep there eye on Simon and maybe help him a little along the way in order to achieve Dracula's revival since the two seem to be in collusion, though their purposes are different. However once Dracula's resurrection has begun they turn around and try to kill Simon. I'm not sure what you have in mind for the trek through a restructuring Castlevania but having the cult leaders as bosses who're attempting to stop Simon's progress through Castlevania before he reaches a weakened yet reviving Dracula, would be interesting concept. Just throwing this out there 
that's essentially what the Herald is, He's a Frequent boss and also a means to draw Simon into traps and such, on the plus side its another character for interaction.
he's a sort of a "Isaac", but as it goes, he'll be a factor in the story.
If you Fight Dracula's Spectre While still cursed, You'll get the Bad (or even worst) ending.
If you Fight Dracula Spectre while uncursed, The Herald will intervene at the end, Sacrificing himself to finish the revival of dracula, thus granting a brand new area.