Both poets are speaking of an America that should be vastly different than it is.  I think that Dunbar and Hughes were radical for their time in that they demanded that the marginalized voices of African- Americans should be understood and grasped by the cultural majority.  In some respects, Dunbar experienced much more difficulty than Hughes.  Dunbar was challenged by the issues of race as well as artistic voice.  He understood that there was a real and valid issue of ethnic condition that had to be addressed in his work, but also felt challenged by the limitations this might hold on his ability as an artist.  In this light, one can see Dunbar fighting both the demons of racial injustice and artistic limitations forced by an exterior condition.  Hughes was able to understand these same forces, but embraced it.  Whereas Dunbar sought to give voice to the condition of those who were silenced by social valences as well as his own artistic creativity, Hughes embraced both dimensions in his writing of racial injustice in so many different forms.  While one might have laid the groundwork for the other one, both writers saw an America in front of them and envisioned what it could be in terms of its inclusion of "the other."