It's not feedback per say like "howling". What you actual are adding both to your voice AND the music is a slight amount reverb.Depends on the quality of the mic and the speakers. I rarely have feedback issues. In fact, my mic is always on and just resting on my console ready to be used... yet nothing get's picked up (just listen to my videos). To each their own though on the placement... I know I am not the only that has them lined up like that though (regardless of my controller being in front)... it really is a streamlined look when all the equipment is lined up like that. I'm sure in certain venues they could run streamlined with the controller, but since I was already on the dancefloor, not much further back I could go.
Try it yourself - stand on the dance floor, and have an assistant talking into the mic continuously, moving from behind to in front of the speakers - you should hear it. It isn't necessarily unpleasant, although it can interfere with intelligibility. However, be aware that if your mike is "hot" all the time, it is doing the same thing with the music.