They can disarm the traps but, even with sufficient Open Lock, they will attack the runic chest instead.
Bug or intentional? If intentional, the entire point of henchmen at level 30 is to disarm and open locks because I'm already dumping points into Leadership. I don't want to dump into Open Lock to open a runic chest and having another set in my inventory specifically for opening Runic chests feels extremely gimmicky. Hopefully this is just a bug; My mind goes to when Runic chests were changed from only being openable by Rogues and something was not adjusted for Henchmen, maybe?