Sennheiser G3 event audio So I work a lot filming events making aftermovies. Often my job requires me to get a master out from the mixer or the sound tech and I am at the will of them so to speak with regards to my audio. Rode Video Mics, Shotguns close to the stage .etc. all provide too much echo/reverb and overall bad audio. When I get master out I rarely have a problem, and usually get pretty good audio. 

However, I have noticed that 99% of the in-house audio is transmitted wirelessly via Sennheiser G3's. Usually the receiver is this Sennheiser rack mount device. All in all something like this. My question is, if I get a G3 receiver couldn't I just get the frequency of the transmitter and 'tap' into the speakers transmitters, and secondly, would this cause an issue for the soundbooth guys?
This is commonly done. 

I suppose with modern digital systems it might be more complicated, but with standard analog systems it should work fine. You'll just need the frequency from the FOH team.