They don't work as WELL on a Mopar. Mopars have a short front spring segment that acts as a pair of traction bars already. Because the front segment is shorter than say a Camaro front spring segment, it is a lot stiffer. This inherent stiffness causes the rotational force of the rear axle to literally lift the body and plant the rear tires. This is even prevelant without a pinion snubber. Add the pinion snubber and the effect is several fold. Adding traction bars to the Mopar leaf spring suspension does not work as well because in effect, the traction bars coupled with the short front spring segment cancel each other out. In order for the Mopar suspension to work, the springs MUST flex. When you add traction bars, you are taking away a lot of that flexibility, while adding a pinion snubber takes advantage of that flexibility and turns it into traction.
