I see older references saying that this node should work with thorns but I’m in training grounds flipping it on and off and watching a skeleton do the exact same thorns reflect damage regardless. This would appear to be another victim of recent summoning damage changes, though since this is a more complicated interaction than say deadraiser not working on summon damage nodes, I am not completely sure if it is intentional, despite having allegedly worked before to boost thorns.
Assuming there was not a reason this was changed, it should be fixed. From what I can tell necro thorns is not exactly overpowered at the moment so can be “helped” without any issues.