Imus the minstrel
If you want Imus's frame of reference read this history of white caricatures of African Americans and then peruse this excellent wiki history of the minstrel show. In short, Imus's reference is Buckwheat, not hip hop. Later in the same program where Imus called the young women of Rutgers University "nappy headed ho's", Imus's sidekick used the term "jigaboo": you can read definitions of that term, written largely from a racist viewpoint here.
Folks who think that what Imus is up to has anything to do with, or is excused by "hip hop" or "rap" are basically ignorant of rap music and American cultural history.
Imus was playing the minstrel. In making those slurs he was putting on black face and playing the minstrel role for his audience based on their, his audience's, perceived view of "black dialect". Now, the fact that many folks on blogs confuse the use of the term "nappy headed ho's" and "jigaboo"...ie. Imus's minstrel act...with the rap lyrics they pretend to imitate is nothing new (from the wiki history of minstrel linked above):
Despite the elements of ridicule contained in blackface performance, mid-19th century white audiences by and large believed the songs and dances to be authentically black. For their part, the minstrels always billed themselves and their music as such. The songs were called "plantation melodies" or "Ethiopian choruses", among other names. By using the black caricatures and so-called black music, the minstrels added a touch of the unknown to the evening's entertainment, which was enough to fool audiences into accepting the whole performance as authentic.
The reason we don't see Imus apologists actually quoting rap and hip hop lyrics as his source material..Ice Cube's ultra-vulgar Givin' Up the Nappy Dugout is probably the most famous use of "nappy" in hip hop lyrics...is that to do so with any authenticity would confront the fact that rap and hip hop have been one long reaction to, rebellion against and explosion of the history of minstrelsy in American culture. One can, of course, debate and disagree with any individual hip hop artist's use of language...and often with cause like in the misogynist Ice Cube lyric above. But to do so, one has to actually pay attention and try to understand what rappers are doing. A real discussion of rap lyrics, including a critique of their frequent misogyny, violence and homophobia, would be a welcome step forward, but that's not what's happening here.
Bottom line, rap and hip hop have consistently rejected guys like Imus, how they view black culture, and everything they stand for. Equating the two is to misunderstand rap as a cultural form. Hip hop, at it's core, is very much a response to how mainstream audience's "hear" and "perceive" black youth culture; to say that bigots will have a hard time "getting" rap is axiomatic. That's the point.
When Snoop Dogg made his much misunderstood and ridiculed statement regarding Imus what he was saying was something about this very fact. Equating the white minstrel show with what it purports to "imitate" is ludicrous and backwards. Rap and hip hop lyrics, for all their frequent offensiveness, do not, as a matter of course, ever refer to women's basketball teams made up of hard-striving scholarship students as "nappy headed ho's" or "jigaboos".
White shock jockeys playing the minstrel for their national audiences...do.
Folks who can't hear the difference between the two things and hence, equate them, need to check their ears and ask themselves why that's so.