Well, if you think it for a moment: Most (if not all) KVM's use PS/2 connectors. So you would need to make the amiga keyboard/mouse talk PS/2, and then make PS/2 keyboard/mouse talk amiga again.
Only after you manage these problems (it should be possible as both converters exist) you can start thinking if it would work.
I know a friend who used PC keyboard/mouse in such setup, he had: pc keyboard / pc-mouse <-> kvm <-> ps2toamiga <-> a4000. It was quite flaky with this setup already.
