anyone ever seen an application where 277/480v was used, using NM? "

I have seen it used ..and we ripped every bit of it out. It was in a HUGE warehouse rite outside of Philly. The place had a drop ceiling with 2 x 4 layins. well over 300 of them. Somebody wired them all with romex, 12-4 romex to j-boxes then three 12-2s to a group of 8 or 10 fixtures. All the J-boxes and wire was just laying on the ceiling tiles and grid. J-boxs were nasty .. lose wire nuts, bare wires... What a mess ... spent weeks in the place re-wiring. In Lots of Places in PA ..ANYONE with insurance can be an electrical contractor, and it shows with some of the work I have seen there in the past 20 years.