Hughes did it. Check out aspects of "The Negro Speaks of Rivers." Hayden did it. Consider those poems where he wrote in the voices of runaways and as Wheatley. Margaret Walker, she did it too...has one in the voice of Tubman.
Dudley Randall wrote as Frederick Douglass. Alvin Aubert assumed the perspective of Nat Turner. And it's not just the elder established figures.
[Related: Persona Poems: A Major Trend in African American Poetry]
Elizabeth Alexander, too, has written in the voice of Nat Turner. Quraysh Ali Lansana as Tubman. Evie Shockley, Tim Seibles, and Vievee Francis have, like Randall, written as Frederick Douglass.
Thylias Moss wrote an entire collection, slave moth, in the voice an enslaved girl who strives toward freedom. Frank X. Walker has written two full-length books--Buffalo Dance: The Journey of York (2004) and When Winter Come: The Ascension of York (2008)--in the voice of slaves.
The title poem for Natasha Trethewey's Pulitzer-prize winning volume Native Guard is a sonnet sequence written from the first-person perspective of an ex-slave turned Union solider. Kevin Young's Ardency: A Chronicle of the Amistad is filled with the voices of enslaved and formerly enslaved figured.
Lucille Clifton has written in the voices of folks who were "loaded like spoons" into ships call Jesus, Angel, and Grace of God. And one of the funniest slave poems you'll ever read is Ishmael Reed writing at the beginning of Flight to Canada in the voice of a clever runaway named Quickskill.
It's fascinating when you think about how many African American poets have written persona poems based on slaves and runaways.