Pretty sure it's Nash on the Crosby album but it wouldn't surprise me to find out that Donovan showed up as well.
"Chet" is really all about the atmosphere. One of the most relaxing jazz albums I've heard but yes, that doesn't always mean it's terribly exciting. Evans seems somewhat restrained but Chet has such a lovely tone (the most beautiful trumpet tone in jazz IMO) that I can just enjoy his soloing purely because of the tone. But I do tend to favor Baker compilations with feature a mix of vocal and instrumental material- that's the best way to listen to him, as far as I'm concerned.