You dont have to pass on the information about if the actor is hidden to the clients. This information replicates automatically when the actor is replicated.
Just change it on the server and it will propagate to the clients.
It would be best to have a server side actor responsible for showing / hiding the actors. It could also keep there reference in an array (a use of object pooling).
Upon enemy spawn it would register with the pooling manager and be added to its array.
The next time you need to spawn the enemy call the manager function responsible for getting an innactive eneny in its array. Activate it, reset it and put it at tge needed coordinates.