It appears the FTX/Orbx autogen files already include the FlyTampa Grenadines autogen data, so I was able to observe full autogen on the Grenadines islands without having to run the Fly-Grenadines_FSX_P3D_AutogenEditor program.
I did make sure to select the "Prepar3D Autogen" option on the Configurator tab for Grenadines.
Looks like this is a workaround for the Grenadines spb2xml crash issue, at least for those who also own FTX/Orbx products.