I can't find any direct evidence, but I wouldn't be surprised if there is a connection. If there is it's different from what you suspect.
Saba (along with sita, tisa and the words for higher numbers such as 20, 30, 40 etc) is a loan from Arabic. Arabic and Hebrew are closely related languages. So it is not a sign of subsaharan African influence on Hebrew but of the influence of Arabic, a close cousin of Hebrew, on Swahili.
Then again, within the Semitic languages, the similarity between "seven" and "sabbath" may just be a coincidence, as I haven't seen anything to suggest otherwise other than the kind of feeling that there is kind of an obvious connection there, but these things can also be the result of coincidences ... so I'd put money on it, but not very much.