Realism can be defined in a number of different ways, and your answer to this question will depend on your particular defintion.
For example, you might define realism as an attempt to represent the real, spoken language (and other customs) of people rather than the idealized version of language that we're taught in schools. In this sense, "realism" is pretty much the same in meaning as "local color." Hughes' play would be realistic in this sense because it uses black dialect.
You might also define realism in terms of a close attention to economic power of different groups of people. The study guide cited below includes the statement "One of the major themes addressed by realist writers is socioeconomic class conflict." In this sense, you can see the racial tensions in the play as class tensions, as conflicts between the ones who own the land (and give the orders) and the ones who work the land (and are expected to obey the orders).