My understanding is BOV's are used on gassers because they have a throttle butterfly whereas diesel dont. If your in high boost and close the throttle the air hits a wall and has nowhere to go except back into the turbo, destroying the impeller, sending chuncks into the engine when you open the throttle again. When you let off the pedal in a diesel the incoming air can still be forced into the cylinders, there's just less fuel to burn slowing the turbo.