Shrock bumper has different mounting points than the regular bumper, so the relocation brackets wont work. Im not sure if Jim (owner of shrockworks) has made any adjustments/extra mounts for an xterra with a body lift or not. You might want to call or send him an email asking him.
I know that before boon dox SASed his rig... he had a 3" body lift and a shrock front bumper. He was able to move the bumper up about 2" because of the way it mounts to the truck (but doing this makes it a little less sturdy). But even after doing this he still had a weird looking gap in between the body and bumper.
The only real way to resolve this would be to have Jim make some different mounting brackets, or fab some up yourself.