I really do not think that wiring a proper optimization system in Playmaker is a particular great idea - why not use Unity's inbuilt culling?
Simply de- and reactivating objects via "Activate GameObject" will actually give you performance drops.
To give you a possible solution for getting all objects inside a trigger :
when an objects enters a trigger store it in a specific array. when it leaves the trigger delete it from that array. When the culling / optimization is called iterate over all objects inside that array until there are none left.
Again, I do not think this will give you performance optimization.
