Well yes you can do this, however I don't think you'd want your audio to be wireless, as static interference could happen & You don't want your speakers turned up then all of a sudden get a flash of white noise becuase the signal is being blocked/deflected just perfectly for that moment.
Wireless video is more common, although i'm not sure who makes the transmitter/receivers anymore. Rat Shack used to have them & Recoton (I believe) used to make them - The Rabbit. These worked ok as long as they were unobstructed, again, anyone getting in the direct path would cause static in the video, I used to use these quite often in my shows especially with clubs with hard to run cable or no where to conceal the cable.
http://www.shoptronics.com/5wiauvisetrb.html
There is a wireless audio/video setup. Although it's not set up for pro-audio, just RCA line level.