The hallow spell prevents undead from entering a certain area:
First, celestials, elementals, fey, fiends, and undead can’t enter the area, nor can such creatures charm, frighten, or possess creatures within it. Any creature charmed, frightened, or possessed by such a creature is no longer charmed, frightened, or possessed upon entering the area. You can exclude one or more of those types of creatures from this effect.
In addition, it has an optional effect to prevent dead bodies interred within from becoming undead:
Everlasting Rest. Dead bodies interred in the area can’t be turned into undead.
Assuming the caster of hallow did not select the Everlasting Rest option, if a character casts animate dead on a corpse within a hallow zone, what happens to the resulting zombie or skeleton?