Hi Ted, linked models can be a bit of a pain to use with any distributed rendering method. One way around issues with using a shared folder is to pack the linked assets into the blend file. Did you know there is a command in blender to do this? If you bring up the command search tool (F3 now in bl 2.80) you can search for "pack", one of the results should be something like "pack libraries". This will pack the linked or appended assets into the main project file.

Then you'll need to resync your scene on all your nodes.

One thing that might catch you out here is that when you do this, if there are any external assets in your linked files, then you'll need to open those files and pack all into the blend file in those files first before packing libraries in your main file. Sadly the function in blender to pack libraries is not recursive, so it won't pack the external assets of your linked/appended assets for you.

Finally if you'd rather use a shared location, know this, others have done this successfully I believe. You need to make sure that the path from each node to the shared location is actually valid and can be reached. Usually with a shared location, there will be a network path to the shared resource, if you're mixing computers with different OS types, then it might be that the path blender has in your client, can't be resolved by the nodes because of its format. I have to say I am guessing a bit here but maybe try using the path to the shared resources on the render nodes in a file browser, if you get problems there then its likely blender will also fail and you need to figure out why the computers can't use that path.

Hope this makes sense :)