I spoke with someone at Stillen about this. Because it is slightly different they just err on the side of caution. It will fit, guaranteed, with little to no difference between the non-Nismo version.
You can see the right vertical plastic diffuser here. In front of the bumper, so pretty much out of the way.
You can see the black horizontal metal pieces here that line up with the top of the bumper. Worst case I've heard that these may need to be notched a bit.