Cambium supports ePMP and PMP100 GPS timing for back to back frequency reuse... there are a couple of caveats however... one, you'll need to make sure you use 2.5ms framing on the ePMP, and second, unless you're using 3rd party antennas with a high F/B ratio on the PMP100 side... that is, if you're using the stock PMP100 advantage AP w/integrated patch, you'll need do some things to reduce the amount of noise bleed off the back of the PMP100 AP... this is more important the lower down in the band you go... i.e. 2.4 GHz will be worse then 5GHz. Some things to do might be to create more physical seperation, add shielding, or use a connectorized PMP100 radio with an antenna that has a high F/B ratio.
For additional information, you'll want to take a look at this ePMP to FSK guide HERE, and you'll want to use the ePMP to PMP100 GPS sync spreadsheet located HERE to get the proper timing settings down.