Yeah, Oakley Hall is far from an unknown quantity on the West Coast. He's more of an august presence, especially at the Squaw Valley Writer's Conferences. I met him up there in 1994 (I think it was). Also met the daughter who was (is?) married to Louis Jones. Sorry for getting off on the Louis Jones tangent, but I was amazed by the Ed Dunkel reference.
This past fall I met Sands Hall, who lives near where Gary Snyder lives--Grass Valley/Nevada City area. She told me that her dad was doing well, still writing, still playing tennis. So yeah, it is kind of a West Coast thing. You hear about people, meet people, read things in the SF Chronicle that are not in the NY Times.
I have read the first two of Hall's Ambrose Bierce "mysteries." I know they are being marketed as mysteries, but really they are good historical novels. The use of Bierce as a fictional character is interesting and is handled well.
None of this has gotten us to "What Walt Disney Knew." My guess is that if it has been published at all it's in an early, probably out-of-print, short story collection. Or possibly it ran in a magazine around the time that you heard it on the radio. Maybe a search of periodicals would yield something.