Fire tusk

Somebody said something resembling an answer I liked, I'll quote off the top of my head here. He said something involving how these guys are fire immune, and how Elemental Reset doesn't transform your fire attacks into non-elemental attacks, how it only takes 100% of the 'fire' damage out of them. They're still fire-based at heart, so enemies completely immune to them still take no damage, while enemies that have heightened resistances/weaknesses take normal damage.

Edit: So no, you can't damage them.