The shock's effect on under/over steer is just in the transient phase. Meaning when you start turning, before the car takes a set. The shock determines how quick or not quick the car takes a set.
An example, if the car is set up with the springs and sway bars to handle neutral. A shock that is too stiff in the front (compression) will intially cause understeer. But once the car it "set" it will handle neutral.

That's as basic as I can get it...the science to this goes on forever!