Not really, if you know the melody. It’s not like I’m making it up myself, which is how I define scatting -- improvisation in the moment, when a singer utilizes their voice like a horn to create new melodic lines.
Yes -- I’m aware of what you state about the Dead. It could be said that Garcia’s awareness and utilization of chord tones in his soloing was more akin to how a Jazz player would solo, as opposed to the more typical (For Rock) approach of overlaying a scale or two over a progression. (The Son’s Terry Haggerty was another). I’m a huge fan of Weir’s playing and know about his admiration for Tyner.
The thing is, for me, the Dead don’t sound much like Jazz. Much of their music is very major-sounding, as opposed to dominant-sounding. They may have been as influenced by Jazz as the Allman Brothers, but to my ear, the sound of Jazz is much more evident in the music of the Allmans -- not only harmonically, but rhythmically. The Allmans swung! Nevertheless, the Dead’s improvisatory approach definitely helped open me up to Jazz.
However, when I think about it, it was actually Stevie Wonder who probably had greatest influence in this regard -- particularly "Innervisions". That really opened my ears, not only in terms of listening, but it made me want to expand my chordal knowledge and understanding on the guitar. I began trying to transpose his piano chords to guitar, which in turn made me realize many of the guitar chords in the Innervisions "songbook" I’d bought were inaccurate. But I digress.
Wes Montgomery's guitar playing is jazz, but he's very lyrical
Your insertion of "but" makes it sound as though lyricism is a rare exception in Jazz. Not to my ear!