Data used on hotspots does not count toward the cap. However when using an XB6 I could never connect to my own hotspot. It always tried to connect to a more distant hotspot. Maybe they have something in place to stop folks connecting to their own hotspots.
I did have a close neighbor who always transmitted the hotspot, often streamed Fire TV on that.
(Of course they may have changed things since I last used it in that way). 🙂