I found this information on the HomeSeer message board. This is for the free jvCaddx plugin.
"jvCaddx Plug-in connects HomeSeer to the CADDX/Network family of alarm systems. You can use the NX-8e 'as is' but for NX-8, NX-6, NX-4 you will need a NX-584 expander. "
So it depends on your systems model number whether you need the expander to communicate with the panel or not.