Methods employed to learn vocal jazz improvisation are the same methods instrumentalists employ. Vocalist will develop their musicianship and employ techniques that instrumentalist use to solo over songs and jazz vocalist use to scat over chord changes.
The teaching model is reminiscent of how Dizzy encouraged Ella to employ scat techniques in her performances. You'll learn to break down tunes and hear the subtle harmonic motion while training your ear to employ sophisticated melodic-development methods and melodic voice-leading techniques.