Chelsey Luger, of Indian Country Today, has written an interesting article about nuances in language which help describe varying degrees of respect.
"What’s the difference, and why does it matter?
It’s a subtlety in language that has the power to evoke varying degrees of respect. The indefinite article (a or an) should of course be used freely when referring to objects - like a candy bar,a book, or an orangutan. But it shouldn’t be used in front of an ethnicity, because it creates a demeaning connotation."