Just Theory Crafting but you may want to see if the lua function UnitCanAttack returns a value on the target, if it shows the target can not attack, you could use OnInteract or on FightsStart event to run a blacklist mob.
Wrobot it self is just a path finder / extensive api. If you want something you have to build it. Or at least give us the name of the server so we can somewhat try to help.