Well, not all Black people are the stereotypical trashy, uneducated, low-class vermin that you have in America. Those give other Blacks a bad name. And Redguards aren't of African descent, so they aren't obligated to have any cultural, racial, physical, etc, similarities to Blacks.
In response to this, I'll repeat what I said before. I think it covers things well.
As someone who is both knowledgable of Redguard lore and an African himself I think I'm qualified to respond to this:
Like most elder scrolls races, redguards are superficially based off of a real life culture. While they diverge in many ways, Redguards are, at their core, a fusion of african / arab cultures. Everything from their language, which is a cross between african and arab sounding words (Hoonding, Alikir, Yokuda, Ansei, I even saw a name in a book that literally translated to something arabic) to their clothing, and their facial structure are based off of these two cultures. Now consider this:
The games Redguard, Morrowind, and Oblivion all used an African voice actor. It wasn't anything offensive, you could just tell by the sound of his vocal cords.
Many races have distinct accents in this game. Redguards could easily have been given an african / arab accent.
I'm pretty sure some of the orcs have black voice actors. How is that less offensive than giving black people black voice actors?