These are two very good poems to discuss together. I hadn't seen the connections before and appreciate your question.
The speaker in Hughes' poem may be male, and the subject in Angelou's poem certainly is female. As I read them, both poems establish a connection between black people and Africa that goes beyond history into myth. Both focus at least in part on the Nile river and the pyramids as well as on reclining along the banks of a river. (Hughes' poem, I should add, perhaps has a wider vision, including more than just black Africa. He includes the Euphrates, for example, which is in modern-day Iraq and isn't connected with black history.) Both deal in metaphoric terms with slavery or, at the very least, with the transportation of blacks from Africa to the Americas (Angelou's poem is much more explicit in the treatment of slavery), and -- perhaps most importantly -- both poems end with a sort of transformation or transcendence; the Mississippi waters turn from "muddy" to "golden" in Hughes' poem and the previously inactive subject in Angelou's poem is "rising" and "striding" at the poem's end.