As I understand it Rewire passes the audio from one DAW to another for further processing, so it could fall foul of the rule you quoted: "Audio must not be touched at all once it leaves the DAW" if any effects or mastering are applied in the receiving DAW.
Midi signals of course are perfectly ok. I believe Rewire2 allows for midi signals to be passed.
I believe this has been touched on in the past, and the consensus at the time was that its prob easier, and safer to simply stick with a single DAW for the competition.