CrgSim supports a very rudimentary flight plan (just location IDs and Lat/longs). This info is not shared with FSX.
CrgSim is driven by variables provided by FSX. If an addon works by setting variables in FSX then they should be available for CrgSim and things should work ok. Some addons keep variables local to the addon and don't share them with FSX. If any of these variables are needed by CrgSim then the sim does not work (at least with respect to this variable). We really like the PMDG products but CrgSim doesn't seem to be able to work with them. Radio frequencies are just one example.
The flight plan functionality could be enhanced but interoperation with PMDG probably not.
Kapock
