In Curse of Strahd,
Note that the Hallow spell has two principle effects.
The first is that it bars the entrance of undead, as well as prohibiting them from charming those on the hallowed ground and removing the effects of charms on anyone who enters the hallowed area.
The second effect, however, is chosen by the caster of the spell from a list of ten possibilities.
Does the second effect apply in this case? If so, is it chosen by the relic or by the priest?
While the first effect will go a long way to excluding Strahd and his minions from entering the hallowed ground, which second effect choice would best protect from his non-undead minions? If the priest were the one making the decision, what would he be most likely to choose, based on what he knows about Strahd’s minions?
Note that Strahd’s minions include bats, rats, wolves, and dire wolves, but also living humans.
Humans could be those Vistani that serve him, but could also include cultists under the direction of the diabolist. I think it is likely that the priest knows about these loyalties and activities.
Humans could also include town guards who are not charmed themselves, but might be acting under orders should Strahd decide to charm the ‘mayor’ or the ‘captain of the guard’, possibilities that I think the priest would consider.
Note also that the relic far outdates the priest, so he is unlikely to have considered making this choice before, and that he is incapable of casting hallow himself or indeed any spells above third level, so he might lack practical knowledge of what his actual choices are.
A good answer will explain why the priest or relic is likely to choose what they would, based on how the mechanics would interact with Strahd’s non-undead minions.