Orpheus, my next music contribution was going to be Ella doing Billie's Bounce. I completely agree with your comments about the appropriateness of scatting some times and not others, and this relates in key ways to the earlier discussion about Moonlight In Vermont. Ella was not only respectful of the song (as you point out), but was (IMO) the only only singer that could scat a solo that doesn't leave me saying "that was pretty good; for a singer". She could scat a solo very bit as swinging and in control of the MUSICAL vocabulary as a good instrumentalist.
http://m.youtube.com/watch?v=cLep2fmY6sw
http://m.youtube.com/watch?v=cLep2fmY6sw