Just found a prestige class in Paizo People Of The Sand supplement called the Living Monolith that grants Righteous Might with DR based on PC alignment:
http://www.d20pfsrd.com/classes/prestige-classes/other-paizo/i-m/living-mon olith
Given this prestige class neither requires nor grants channeling, cure/inflict casting, or even spellcasting, I'd argue that it provides more "evidence" to support the validity of Wraithstrike's and Gauss's suggested houserule that an Inquisitor should also get DR with the spell, type based on sacred or profane judgements. Especially, as Inquisitors have no other spells that I know of, anyway that are "nerfed" / don't work for them as they do for other classes.
Wish Paizo would respond to FAQ & rule on this...Also for Druids with the Growth Domain, which have a similar lack of clarity.