I've set fusion to run in Unity so I get the best of both worlds throughout my day. Unfortunately when I'm in Unity, the files I have on my PC desktop are not visible - but my Mac files are. Is there any way to address this?
No, at least not through Fusion and IMO it is a bad practice to work with files directly on the Desktop and files should be maintained in a logical hierarchal folder structure in a more centralized data store. IMO if you want to use the Desktop as a central point for working directly with files then shortcuts are better leaving the original in the My Documents folder structure and in either case if you find that you're Desktop Centric then Unity is not conducive to that concept.
That said if you really want to use Unity and you want to have more direct access to data stored on the Guest OSes Desktop then share the Windows Desktop and then create an Alais on the Mac Desktop to the Windows Desktop and while it's not the same as mirroring in the opposite way that Fusion has a feature for it is the best suggestion I have to offer.