I had a GCP for a while and Tap Tempo worked fine for me, but from what I remember you have to do a few things:-
1. Set the CC on the Factor and GCP to be the same value eg 31
2. Set the GCP instant access switch to transmit on the Midi Chanel of the factor
3. Set the GCP instant access switch to momentary
That should be it
It has to be momentary as the factors see tempo pulse as any cc value of over 67(?) so if you have a latching switch the CC values are typically 127 for on and 0 for off… So the factors would only see every other press as a beat.. If you only give 2 beats as you tap temp the factor would only see one neat and if you give 4 it will only see 2 and give you half the bpm you were expecting.
On the GCP you can get arround this, not so on the rocktron midi mate.
I only tried this on internal switches and not external ones, so I would try the internal ones then see if the external can be set to momentary or there is some comparability issue between the GCP and the external switch eg the wiring is wrong polarity.
Hope that helps