Either look into it in the engine source code, for the rendertarget class (whatever it’s called), or ask someone who has looked into the engine source code. Sorry I’m not one of those people yet (maybe someday!)
You can see if it’s nothing more than a pointer based on how the class and its variables are declared.
Also look into how replication is done . You’ll have to see how Blueprints expose the C++ behind that for Custom Events that are set to replicate and when variables replicate. Find out if they just pass it as-is or attempt to get a unique ID for network to match it up with the same object on another machine.
Might be easier to ask someone like eXi / Cedric Neukirschen