vocal arrangements

i heard the soundtrack to this film years ago and loved it. today i finally got around to watching the whole film and it reminded me of one of the reasons why i love the music so much: the vocal arrangements. in a lot of the numbers, the chorus is used sort of as an extension of the orchestra, adding instrumental detail rather than just harmonizing with the main singer(s). good examples are the second refrain of "blue skies", "pack up your sins and go to the devil" (that "dadada wah-wah-wah-wah" near the end is delicious omg), "my walking stick", "everybody step", "easter parade", "heat wave", and the ending performance of "alexander's ragtime band". i've seen some other musicals from the '30s and '40s and never really noticed vocals like this in them, so it stands out even more to me.

anyway, any ideas who arranged the chorus work for this film? i noticed there are quite a few people credited for various musical work. alfred newman, maybe, or fletcher henderson? i'd love to know just so i could seek out more of their work, see if they arranged vocals similarly in other movies.