Looks like you can't apply any debuffs to the trial dummy, so Ravager will never proc. Tested with Pierce Armor, Razor Caltrops and Unnerving Boneyard.
That would make sense, the trial dummy already has all debuffs applied by a reduction to its overall resistances. Allowing extra debuffs would result in that debuff being applied twice in effect. It would mean that the ravager set will not proc though.
This is why ravager is now a terrible set. If a target already has named debuffs of longer duration than you’re applying then the set will never proc. This was reported on pts but made it through to live.