One of the first releases on Hit was by the pseudonymous "Arthur Fields" on Hit 7023 with "Der Fuehrer's Face" (1942). That one also had no connection I can see to the singer Arthur Fields who recorded prolifically in the 1920s. Another pseudonym, Peter Piper, was probably inspired by the Mother Goose verse, "Peter Piper picked a peck of pickled peppers". So just because the Will Kelly Band sounds nothing like Roosevelt Sykes means little; it could still be inspired by Sykes' nickname.
Actually, I think you are right about the ODP entries, 100%. Which uts us back to square one as far as who the vocalists are. I noted the use of the Willie Kelly pseudonym by Roosevelt Sykes, too, but I think that is pure coincidence. Noting on this record reminds of Sykes. The A-side vocalist has a little bit of a Johnny Mercer feel to him and the B-side vocalist reminds me a little bit of Dick Robertson, but I don't think either of these vocalists are who they remind me of.
I actually think these are not initials since the letters are in lower case ("vm") whereas the ODP usually lists the initials of singers in capitals, as, for example, for HIT 7029b, where "vED" means "vocal Emil Davis".
I also see only "v." listed under HIT 7049, which probably means simply "vocal". The abbreviation "vm" appears at HIT 7039. It must mean "vocal, male". There is somewhat of a parallel notation for HIT 7035 "Daddy's Letter", where it says "v fem", which can only mean "vocal, female".
I wonder if the pseudonym Willy Kelly may have been a homage to pianist Roosevelt Sykes, who used this pseudonym when he recorded for the Victor label (source).
The ODP lists several records made by Willie Kelly AHO on Hit. Only one offers any hint as to who the vocalists might be. The initials VM are given for the vocalist on that record.