Brown's survey of recordings by celebrities who are not celebrated as singers missed one of the best: Yul Brynner's 1967 Vanguard album "The Gypsy and I," in which Brynner's mahogany baritone mixes stunningly with his guitar work and that of his long-time music partner, Aliosha Dimitrievitch. I've had the album 20 years and still try to listen to it every week or so.
I'd like to have read a little more about the cover-pictured albums by Jeff Chandler and Robert Mitchum. Chandler had a Vegas act for a while and, while Mitchum's calypso record may not be much, the one you pictured, "That Man Robert Mitchum Sings," covers Dean Martin territory almost as well as Dino.
And then there's those two fun albums by Ken Curtis, "Gunsmoke's" Festus Haggen, who just happened to be Sinatra's replacement with the Dorsey band once upon a time.
Now, to undercut the validity of my opinions, I should mention that I own seven Claudine Longet albums because I enjoy them.