Correct. Jaco first appeared on Hejira. He and some other jazz guys were in her backing band for the Shadows and Light live album and video, which is great stuff. The video is on YouTube in its entirety.
The album didn't have Jaco, but as always, she had a great supporting cast. From Wiki:
Joni Mitchell – vocals, acoustic guitar (tracks 1–4, 9), Moog (2), piano (5, 9), keyboards (7), ARP and Farfisa (10)
Victor Feldman – electric piano (1, 5), congas (4), vibes (5), keyboards and percussion (6)
Joe Sample – electric piano (3), keyboards (8)
Larry Carlton – electric guitar (3–5, 09)
Robben Ford – electric guitar (1), Dobro (4), guitar (8)
Jeff Baxter – electric guitar (1)
James Taylor – background vocals (1), guitar (6)
David Crosby and Graham Nash – background vocals (1)
Max Bennett – bass (1, 5–8)
Wilton Felder – bass (3, 4)
John Guerin – drums (except 2), Moog and arrangement (6)
The Warrior Drums of Burundi (2)
Chuck Findley – horn (3), trumpet (6, 8), flugelhorn (7)
Bud Shank – saxophone and flute (3, 6), bass flute (7)
Dale Oehler – string arrangement (5)