There are still a number of ways to take out a hacked spiritomb:
-Using gastro acid or worry seed gets rid of its ability.
-foresight, odor sleuth, or the ability scrappy gets rid of the fighting immunity, exposing the weakness he gets from being a dark type.
-Using Rampardos or pinsir, or any pokemon that would have the ability mold breaker.
-oddly enough, for some reason the move fire fang hits for some reason.