Alright, BoM, p. 89, Holy Hatred, plus Heresy Begets Retribution, p. 7. Heroine of the Order.
Do these stack? I would accept that they do, as Holy Hatred effectively reads that they do have the hatred talent against "any target that is not a true servent of the Imperium of Mankind (GM's discretion)," and Heroine of the Order just requires the hatred talent to provide sanctified, proving(3), and auto confirm righteous fury.
Obviously, being ascension level, its certainly legitimate for a PC to really crack open the difficulty curve if they play their hands right, and such talents do make it difficult to perform an investigation in secrecy.
Just that there is a feeling in my mind that this is pretty heavy munchkining. How do others classify "true servants"? Is this humans only, or can warp entities/xenos be included as not being "true servants"? Obviously this can get out of hand real quickly (other ascension level classes force to pick out mutants/heretics/daemons, so allowing one to pick hatred(anything I don't like) is a bit extreme). I'm thinking they must be at least human for this to count, but can certainly be broader than "heretics," and mean any individual who is not as faithful as a SoB (basically anyone without Pure Faith, at least in my book).
Anyway, given the access to other hatred talents, its not like the Celestian's actually are the problem with how cray Palatine's can become, but it seems like an easy way to justify never taking hatred talents, getting Holy Hatred, and using that to allow Heroine of the Order to get crazy.
Note that I am coming at this as a GM, with a player who is possibly interested, not even committed to playing a SoB (and the game would start at rank 4, so its not like this is even immediately an issue)