"I would have to say yes. I have a 2-port KVM for two boxes I have at home, and the image quality is perceptibly different when I'm using the KVM with that monitor vs. when I'm not. Mind you, I am using a cheap KVM, and with VGA cables, i.e. analog signal.
On the other hand, I expect that if you had a good KVM and were using DVI-D or HDMI cables instead, each of which sends a digital signal, then you shouldn't notice any degradation of the picture quality."