A few related questions:
What if the GM wants to have NPCs just make the Willpower tests to activate Dark Gifts? I like it because it lets NPC Heretics generate Bleed, and if NPCs don't have to roll, then there will be no Bleed. Plus, I feel like the Symmetry is fickle enough to say screw you to its own followers and not always work. The GM could always spend DSPs as normal for extra d20s on the Willpower test. So, I think I've answered my own question--that would work fine.
Second, what if you have a Heretic temporarily working WITH the PCs? Should that NPC use the "ally NPC rules" and generate DSPs or should the Heretic have to spend DSPs? What if the PCs don't know the person is a heretic and you don't want the rules giving anything up?