Well perhaps. There are many dialects to Ebonics. While the ‘’high’’ dialect would be used thus ‘’He be’’ or Mofo be doin’’’.... other ‘’lower’’ forms drop the pronoun he/she and is thus ‘’be doin’. Also other forms of the phrase you point for example is the universal ‘’Know what I’m sayin’?’’. A more idiomatic expression, at least to my knowledge here in southern NJ is “Why you don’t be doin’ that?’’. As in “Why are you doing this?’’ Or ‘’Would you please stop doing that’’.