Answer:
I think the "jazz chantings" you are probably talking about is what is referred to as scat singing. Many jazz artists in the 1930s and 40s used this method of singing while mid-song. A scat is a form of improvised nonsensical words and noise put together to, in my best understanding, intensify and put focus upon the various instruments and what they are doing. A jazz musician usually performs a scat in a clear breakdown of a song and finishes before the band explodes with the energy of the song when it comes back in. You could probably hear a good example of this in various jazz songs from that time period.