RasPi Zero W Keyboard emulation works fine except:
At boot, older PCs hang during POST if the keyboard is attached via KVM.
All other scenarios (booting without Pi connected, booting with Pi connected directly to PC not KVM, using kvm.py to switch KVM ports) work fine.
Attempts to read reports from keyboard during boot yield no data. PC doesn't seem to be waiting for keyboard.
I didn't have any issues with scroll lock when I was still using it. That was the key my KVM used to switch. I haven't used it for some time, though.