Okay, the latest chapter had the biggest hint so far. He says not to underestimate those "idiots" since they live by the "will of fire." This means he understands the concept and knows of it. Now, not even everyone in Konoha knows about that shit so i think this was a subtle hint on Kishi's part that he's definitely connected with them in some shape or form. The only question is who showed him such a thing. Was it Yondaime, Sandaime or does it go way back before them?