When I had this conversation at Fl IAEI the consensus was if the exterior box was inside the wall it was OK to use the NM, it got a little more questionable if it was a surface mounted pancake but if there was any raceway involved NM was a tag.
The real gray area was a surface mounted bell box served from the back, but again the answer was usually no. It got into questions about if the back of the box was caulked into the wall and how the box was served.
