Looking at a small restaurant which the architect has classified as a type V-B, which seems to indicate a non-rated fire construction according to 518.4(B). Is type NM cable allowed providing the walls & ceilings have at least a 15 min fire rating as per 334.10(3)?

I would ask the AHJ for my area if it is ok with them before starting to wire. Just to be on the safe side. Now here is my personal take. Rats like to eat at resturants. And they like the sheath and insulation of romex cable for desert. I use mc or emt when I wire resturants even if I could use romex for that simple reason.

NM cable would be permitted.

I'd think it would be OK, but I'd still check with the AHJ - some frown on NM in commercial occupancies, even when they allow it for resi.

I wouldn't care if they frowned or not. Unless there was a legally adopted amendment to the code, I would use it.