I recently answered a question along the same line as this one about how energy resistance affects regeneration, but sadly I have a new variation of it.
My question is about undead, their negative energy damage, and the worst part, their Con drain from natural attacks.
I am currently playing a character who is energy swapped; negative heals them and positive hurts them. I was attacked by a wraith and its spawn. So every time one of them beat my AC and touched me (which was frequent), I wasn't injured by the touch but I took the Con drain. I'm now wondering if that ruling was correct.
Since injury poison does not affect you when DR negates the damage, and energy damage shouldn't turn off regen if it doesn't hurt you, then shouldn't you be able to ignore Con drain because you didn't take damage from the attack?