On opening a file in InCopy CC19, CC18 and CS6 all layers are visible, no matter if any were set to be invisible in InDesign.
It would be helpful to have a button within the layer palette to set all layers to (in)visible as given in the InDesign source.
It would be even better if InCopy had a preferences setting that would allow you to open all documents with the visibility as given in the InDesign source.

This would give InCopy user not only access to all layers, but also to decide whether they want to focus on what the lay-outer wants them to see.