TIL, thanks for the confirmation!
Quote from Talyn_Rahl
I do agree that thorns most likely won't be viable for some of the same reasons you list. Specifically because there's no thorns dmg modifier on offensive abilities. Would be cool if on command skeleton/skeletal mage, there was one...
I was just using Invoker's as an example, to illustrate that you need more than what Necro currently have to make Thorns viable.
So would LoN Petthorn be viable? Possibly, but with (so far) no runes for any skills that support Thorns (like used in LoN Pony), I still think the damage would be lacking.