I think by default the Blood Guard would have to be something else.
Despite the fact that i don’t see any theological points that would put them directly at odds with either large religious organization. The secular hierarchy of the Blood Guard is centered in the Far West. And they are not integrated into anything else. What little we know does not suggest that they want to join with other potentially compatible religious groups. The Deathmongers at one point tried to, or at least proposed, integration between their organizations and were rebuffed.
The Blood Guard are not Mother Church, and definitely not Kalindruhl.
