Nope. At worst, some equipment can induce hum or noise in a power line. Assuming your speaker is three prong, (grounded plug) it would probably be better shielded from power line issues than his pedals. Now everybody makes their own choice when they plug in. My equipment is on the other side of a power conditioner unit. Perhaps his should be also. It sounds like he's trying to scapegoat you for his own shite setup. I have powered speakers and have definitely plugged them directly into the same source as various guitar effects with no ill effects. Unless I am missing something here, it sounds like he has a short to ground in a pedal.