Sure. Basically whenever you add a
UPROPERTY()
UObject* SomeObject;
or a
UPROPERTY()
TArray<UObject*> SomeObjects;
and also for each UObject that you have created, you are increasing the number of things that the garbage collector has to traverse whenever it performs a garbage collection.
So, if you have some pooling thing, and allocate 1000 objects up-front before they are used, or only have some fraction of them being used at any point in time, you still pay the full cost for the GC having to check them while your game is running.