You will have to demonstrate this, not just speculate.
The issue that I have raised comes down to the fact that Category called OST_Viewers is not present in Dynamo’s Categories dropdown, and it fails to pass through their internal constructors. That makes it impossible for me to create a new Filter and assign it to that Category.
Now, Dynamo has a Category called OST_Callouts but for some reason that doesn’t seem to return anything, as in actual Callouts are of Category OST_Viewers not OST_Callouts.
Both of these are valid Categories, and using a OST_Callouts when creating the Filter in Revit UI seems to map somehow to OST_Viewers. They must do that manually in their code or something. That’s not part of Dynamo and has nothing to do with Dynamo. I am speculating because the behavior doesn’t match what I have experimented with.