It's not possible to use third party plug-ins inside any individual instrument plug-in from any vendor.
You can use the FX's the individual plug-in have, the way the plug-in allow.
If you have a host like a DAW, then you can apply any outside FX plug-in you have to the end output from your instrument plug-in. That output could be dry, so you can build your own FX chains as you like outside the plugin.
An application like Analog Lab can also add FX to end outputs as a host. But still not add them between the instruments internal FXs.
