Well in typical Revit fashion this is something else that they know about but choose not to fix. I finally figured out (after wasting hours) that there IS a way to get this working, even though it's an annoying set of hoops to jump through.
You have to nest an annotation symbol into the family which becomes a massive pain in the *** to get the size of the annotation to relate to a real world size. This is far beyond annoying but at least there's some way to get fills to show up in plan and actually print.
In the view
When printing it's now visible!
Thanks Autodesk for leaving this bug for years and years. It's time to fix these sorts of issues. LET US USE FILL REGIONS DIRECTLY IN ALL FAMILIES!
You guys should be working to make this software work smoother not more disjointedly.