Wendell Pierce will have a role in Breaking Dawn, but Summit has not given any info as to which character he will play yet. However, in a recent interview with Rolling Stone, he did reveal that he will be playing a human:
Is it true that you’re going to be in the next Twilight film, Breaking Dawn?
Yes I am. I am not a werewolf, and I am not a vampire. I am actually one of the few human beings in the movie.
Read the full interview here.