Haven't seen it done yet but that's not to say it hasn't been done. I can't imagine it looking right due to body lines, I think of the work people do to make the NBS Esky clip look right on an OBS. Maybe if you shaved the body lines on the rest of the truck, but I hate seeing that, looks too slab-sided, plus the few times I've seen that done it was horrible quality work. One dude covered the whole side in bondo.
Something to think about is the whole bedside on a NBS is fiberglass, not just the fender flare, which is part of the whole side. To me that seems less sturdy but what do I know? Guess I've seen too many OBS stepsides busted all to crap on areas besides the fender flare and that makes me feel like all-fiberglass rear fenders are a bad idea.
Richard