it should work, if i remember right back in the day when i was learning hardware. keyboards and mice use a different signal and i think now the chips that control the xy functions and the keyboard can read between the 2 while both connected, thats why its a combo port. the only thing i would worry about is the power, i know ps2 ports dont use that much but from experiance when accidently removing a keyboard for a ps2 i blew the chip and had to go usb. so i be wary of that.
best thing to do (im going on memory in work i fail) is to look how the combo ports work google it.