Today the headphones out are routed to the Main out, and also master eq on both Main and Monitor are Pre Aux in, so it will not affect the signal (aux send from the PA mixer).
If your stereo monitor mix are connected to the AUX and Alternative input and your IEM are connected to Monitor out in stereo the Kemper can act as a IEM mixer.
The only problem is that you don't have any output eq to shape the sound of your IEM system.
If the Monitor eq was placed after the Aux/Alternative inputs you use the Monitor eq as a master eq to shape/compensate for the freq respons of your IEM.
Another bonus is that he internal headphones amp in the Kemper could be used as a backup if you wireless IEM fails, just plug you IEM into the headphones out of the Kemper and you get the same sound..
So it would be a win , win situation. 