Interesting choices by the OP.
Have heard of about half of them.
Didnt know that the National Geographic guy ever sang.
Lorne Greene's 'Ringo" was spoken, not sung.
But he certain had that "voice of doom" as he was called when he worked for the canadian news radio system during the first half fo the war ( when it was his job to announce all of the allied defeats before the tide of the war started to turn).
Always loved Enzio Pinza on my parents copy of "South Pacific".
Micheal Buble is a good modern specimen in the bel canto traditon.
In the rock/country/soul tradition Roy Orbison has an amazing voice, as does micheal clayton thomas of Blood Sweat and Tears.
The perfect male soul singer in my opinion was Teddy Pendergrass ( smooth and raw at the same time)- but - the list of great soul voices is long: Smokey Robinson, Al Green, Issac Hayes, Barry White,Luther,
My mom said that her two favorite vocalist of the 80's were KD Laing, and Boy George.
Both good choices. Both are gender benders.
Many singers who did not bend their gender as people did bend their gender as singing stylists (ie men influenced by women).
Maurice White of Earth Wind and Fire has stated he was influenced by female jazz vocalists like Sara Vaughn.
The brothers Gibb switched from striving to be clones of the beatles to striving to be clones of American Philadelphia style soul singers at the end of the sixties.
Two friends of mine I was entertaining at a party were both enraptured by an album I played which they both independently declared to be "the best beeGees album theyd ever heard".
It was not a Bee Gees album at all, but an album by Earth WInd and Fire!
It was the first time I ever thought of the Aussie brothers Gibb in the same train of thought as Earth WInd and Fire.
Hey if you're gonna be a clone- clone the best! If immitating the best White band of the sixties stops working , why not switch to imitating the best Black band of the Seventies?
The Bee Gees high falsetto harmonies do sound not unlike the Maurice White lead high falsetto vocals for EWF.
The black female band that beyounce got started in, Destiny's Child, did a great renditon of the Bee Gees 'Pure Emotion" decades after the original. So good music goes back and forth between gender lines.