A couple potential bugs with the Natural Elementalist edge:

First, I am hitting druid-summoned mobs with pillar of lightning. It seems that I should not be, given the Natural Elementalist helpfile. Bug?

Second, Natural Elementalist has absolutely no effect on fellow outlanders notwithstanding the edge description, which suggests it should ("does not affect nature's creatures"). Bug?

If it is not a bug, but rather a matter of game design, I have to say that Natural Elementalist is WAY less useful than Golden Grimoire if Natural Elementalist does not prevent your area spells from hitting your Outlander cabalmates. Perhaps someone could reconsider?

Do you remember which druid mobs, specifically?

Regarding your second point, it is by design that the edge only works on NPCs.