Ok, test done.
First of all, I'm using the JMK Modulation taptation board:
http://jmkpcbs.com/wp-content/uploads/2014/03/Modulating-Taptation.pdfI realise this is not the optimal way to perform tests but all aspects of the board (PWM, Tempo switch, manual tempo pot) seem to be working as expected.
I disconnected the board completely from the Echo Base (which in itself is working perfectly). I connected the DMM to pin 5 of the digipot and to ground.
The manual tempo pot connected to the PCB measures 98.5K.
First off, I noticed that tapping at 2 second intervals does not work, I had to be much closer to the max value of 1125ms for the tap to register (as already noted by blearyeyes).
The highest digipot value I was able to produce while tapping was 78.4K. When setting the max tempo manually the digipot measured 80.1K.
Judging the LED is obviously difficult but it seemed to sync well with the tempo I was tapping.
I'm guessing breadboarding the digipot to measure it isn't very complicated, If I get instructions I'd be happy to do it.

/Magnus