The 5100's for the front have adjustable spring perches that allow you to set the amount "lift" to one of four different settings so no need for spacers. The rears would need a spacer if you wanted some extra lift.
If you're talking about "stacking" spring perch lift plus the 2.5" spacer, I wouldn't recommend it. About 3-3.5" is the max front lift before you run into all sorts of problems with alignment and CV angles.