This one is interesting. If your app does something more than just tethering, it will likely be approved. Your app should change the data in some way for the receiving machine. Automotive telematics systems do this already, for example they use apps to stream music and map data to the head unit (pandora, gmaps) while basically reformatting the data for the head unit.
In other words, don't create a general tethering app, but a specific "service" for another device.
In other words, don't create a general tethering app, but a specific "service" for another device.