I'm wondering what is this type of vocals, what is the humming with the voices instead of singing words called ?
It is called Scat singing.
In vocal jazz, scat singing is vocal improvisation with wordless vocables, nonsense syllables or without words at all.
It is pretty common in Jazz. Singers used it to 'solo' (cause they had no instrument).The song you provided is jazzy so I think scat singing is the correct term here.
Here are a few examples:
This falls under the 'wordless vocals' category:
Not exactly scatting, but they are both wordless vocals.