I cant think of a barbarian unit that my wardogs havent massacred, heck ive sent them against generals and they still pull off the win. I assume they would suck against strongly armoured units like cataphracts and roman infantry but ive never tried. also i doubt they would do anything against elepehants. Anyway a strategy i like is to send them right in the middle of the enemies line, they will probably kill the unit i send them against and instead of chasing the survivors they will get stuck fighting the other infantry and missile troops.