For me, vocalese usually stands or falls on the merits of the lyrics (and a stipulation to a "pop" estheic at some point or another is granted w/o objection). On those grounds, Jon Hendricks scores more often than not, and Eddie Jefferson, for whom I used to have a great deal of love, is starting to fade. Exceptions to both are there, though.
Scatting, though, I dunno. When jazz was a more purely rhythmic music, hey, it was hard to fuck up (although many did anyway. There's some in every crowd, I guess). But once the harmony got more complicated, the need for a concurrent maturation of the scat didn't seem t keep up. Dizzy, Moody, Hendricks, a few others dealt. Not too many more. And then there's Betty Carter, whose scatting isn't really "scatting" at all. She's inhabiting the space with her voice, if you know what I mean.
Now, with post-bop and free firmly behind us (or getting there), what's the need for "scatting" per se? Just sing dammit, whatever that means at any given time. To paraphrase Monk, you got a voice, use it.