Now it can be told!
This is information revealed by the creative team for "Journey Back to Oz" as they discussed the making of the movie during their commentary on the DVD.
Although Danny Thomas is credited as playing the Tinman (sic), in fact he only sang the song for the character. The actual dialogue was performed by Larry Storch (listed in the end credits under "Additional Voices") doing a bang-up Danny Thomas impression.
"Only a Sith deals in absolutes" is an absolute statement.