Hi Michael- you can insert linked files so that the added layers show up in the regular default layer view or you can insert as reference layers - both are useful for different workflows.
" When you create a linked block definition, specify one of two linked block definition layer styles.
All layers for the linked block definition are saved in the active model. All layer attributes, including rendering material, can be edited and are saved. For each layer in the linked model, if there is a layer in the current model with a matching short name, that layer is used, otherwise a new layer is created.
The layer tree from the linked model is added to the current model as reference layers under a “grandparent” layer with the same name as the linked file. All of the added layers are reference layers. Only the on/off, locked/unlocked states and the layer color can be modified.
For an example, see Wiki: Imported and linked block layer names."