Since they're not 88.1-91.9, are they exempt from the non-commercial requirement?
Yes, they're exempt from the non-commercial requirement. Not as much because they're below 88, but because as far as the FCC is concerned they aren't an FM station.
For FM, a band of frequencies (as you cited, 88-92) is reserved for non-commercial use.
For TV, there is no such band. Instead, spot channels spread around the dial were reserved -- channel 2 in Boston, 25 in NYC, 11 in Chicago, 9 in San Francisco, 28 in LA, etc.. If channel 6 isn't reserved in your community, it's perfectly legal to use it commercially.
That, and there never were non-commercial reservations for low-power stations like this one. ALL of them can legally run ads.