I can't see why it couldn't then have the Lawful property weapon, if it better fits the npc background. This would allow for even more player variety, as neutral evil and lawful evil could use it without detriment. Most monsters are chaotic (evil) anyways. The only negative is that a chaotic party member can't use it without a "level" loss. Does the game really need a holy weapon? There may be the occasional DR that is troublesome, but often there is an alternative damage type like cold and silver, that can bypass. Further, the DR is typically 10 or less on monsters where there is no alternative type- and the lawful weapon is still adding 2d6 damage to a chaotic creature.