You don't need
I just read in the i386 distro FAQ that openbsd is sensitive to kvm switches adn I had it on a kvm at work....heh, keyboard ok but mouse funny just as it says....time to get a seperate mouse I guess......looks liek alla systems go exect for that (although fdisk is much more familiar to me than the openbsd way of disk partitioning)
The only issue I've ever run into with my KVM across openbsd, linux, and windows systems is that the mouse ports are ps/2 and the KVM only supports a 2 button mouse. The end result is the scroll wheel only goes down :P (note all the systems except one are i386 and the one is sparc64)
For that matter try unplugging/plugging a ps/2 mouse into systems in windows/X and get really to watch the hilarity. I would suspect a lot of these issues would go away with a KVM/computers that only used usb mice.