Only had a Mac USB keyboard and an ancient logitech mouse to play around with, but seems that typing in text fields works fine, most other keystrokes are ignored. Hitting control-option-f1 seemed to immediately darken the touchscreen, but that was about all, it came back on in a few seconds.
Mouse behavior was more than I was expecting, the scroll wheel actually worked for zooming in / out in the nav app! The cursor was indicated as a small blue dot.