There are two XLR jacks. The shotgun is plugged into one. I think sennheiser has a wireless lapel mic and hand mic that you can toggle between the same receiver. So you could have your shotgun in one jack and your wireless in the other. But could only use one of the wireless mics at a time. So to answer your question the shotgun occupies one of the XLR jacks so if you want two wireless mics at the same time you will have to disable the shotgun.
I was hoping that I could use two lapel mics, then quickly turn them off to pick up background sound. Perhaps they make a switchable connector for one of the lapel mics, so that I can plug in the shotgun too.
It isn't safe to unplugg or turn off an audio channel while recording. Better to use a mixer and handle things there, otherwise you could get a loud noise on both channels.