I doubt it because either Kouichi/Touya said that they had never seen an Ido'ra before, not even in the 'other world'.
Well, if I understood the raws correctly...I'm pretty sure he is.
You mean the raws up until 108? I've seen them, too and they don't hint that he is a Shinma warrior.
I think the guy with the headphones is definitely a reincarnation of one of the six sacrifices ren used which are the shinma warriors. I mean its possible that the headphone guy literally said that he is annoyed how loud the two misaki people are, it also make sense if he is one of the shinma warrior and why Koucchi or Touya didn't recognize him as shinma warrior but as an Id'ora because his Divine Beast could be also defiled like what happened to Hazuki since he/it was used by ren to do a bad thing.
I bet Nakasawa is a new Shinma warrior.