Okay, I'm using MIDI-OX to test both the hatKAT and a generic volume expression pedal to compare (calibrating again when I switch, of course). The Zendrum receives/sends no signal until the hatKAT is depressed more than half way. With the volume expression pedal, the Zendrum sends/receives a signal throughout the full range of motion of the pedal. I'm afraid the problem (or limitation?) is with the hatKAT itself, which is a shame because I really like its spring action.
Alas, I haven't purchased ZenEdit yet, it's on my list to do for sure. The Nord Drum 2 doesn't have a hi-hat control input, just 6 trigger inputs and MIDI. So I'm trying to use the Zendrum to be the bridge from the hatKAT to the ND2.
I figure at this point we've exhausted the Zendrum end of the cable, thanks much David and DrumWagon for your help.
I wonder if there are any users with specific experience with the hatKAT to tell me if this is just how it works or if it's malfunctioning?