It was the first tv show with a black actor or actress as the lead role, though the role was that of a household domestic servant.
I've only read about the Beulah show and have never seen an actual episode, because few copies exist. It was produced in the days of kinescopes, before videotapes, and they only way to preserve a live performance was to make a movie film of a tv monitor...hence the poor images (as you see on "Honeymooners" episodes). The first series that was FILMED (like a movie) rather than presented live was "I Love Lucy", which revolutionized television and created the rerun, since the end product was a motion picture-quality film that was superior to kinescope.
The reviews I've read portray the series as an early variant of the later "Hazel": the housekeeper is the only one who knows what's going on in her clueless, affluent employers' households. But given the times, they probably had to be very careful not to portray Beulah as being way smarter than her white employers. With Hazel and Shirley Booth, without racial lines to cross, it was easier to show Hazel outsmarting "Mr. and Mrs. B" on every episode.
The reason "Julia" with Dianne Carroll was such a big deal in the late 1960s is that for the first time the lead black character was a professional (a Navy nurse, in this case) and not a domestic servant.