Yes, they work together, but there is no enhencement in all of the FXT's PFJ,PNW,NRM,CRM areas, as these Orbx scenries covers all!
Some say, FSX runs a lot better if it's leaner and meaner.
Well, I think it depends on the system. I have UTX Can-USA-Alaska and GEX NA installed (before I ever had FTX-sceneries) and I leave them on my disk.
They are useful when flying out of FTX-land.
Dieter