My principle question is,can I safely use the pattern coat system over the top of this to get the desired finish?

I would agree that you should well be able to skip a step by not using the pattern coat primer and instead flatting a good finish onto the XCR Epoxy Coating Resin. You'll find that because epoxy is so much harder than polyester that it will take longer to flat and polish compared with the Pattern Coat Primer however, unlike many other epoxies, the XCR resin will polish up to a high gloss, given time. The extra-time polishing the XCR will probably be compensated for by the time and money saved by not needing to use two resin systems to coat it, as you would if you wanted to use the Pattern Coat Primer.