You don't need to have every monster to send nothing to a manager FSM, if I got your issue correctly. Or, wait... Exactly, what does this MorphCreature action do? Does it somehow change your monsters (as the name would suggest)?
Now, to call a function from a custom script, you might want to use 'Invoke Method' action, although you would have to specify which GO has the script where the function you want to call is (I'd think is your monitor). If you, by the contrary, want to have a reference for an FSM, declare a public PlayMakerFSM variable in your script, so you can drag&drop the object containing that FSM to the inspector. You would have access to variables, events, and such data.
Hope this helps.