A creature with an alignment subtype (chaotic, evil, good, or lawful) can overcome this type of damage reduction with its natural weapons and weapons it wields as if the weapons or natural weapons had an alignment (or alignments) that match the subtype(s) of the creature.
An arrow demon, for instance, has the chaotic and evil subtypes, and thus can overcome damage reduction as if its weapons and natural weapons were chaotic-aligned and evil-aligned.
