Just looking at the photos from the archives, I'm sure there was racism in the history of buggy (though that may have been a school-wide policy or something - the 1920s photos look pretty white). But at least for recent history, I don't know of anything (except for Compubookie's comments, which have often been racist, sexist, anti-Semitic, anti-LGBT, and had plenty of other issues - though Compubookie has been strongly rebuked for it on this site several times). If buggy is anything as a whole, it tends to be anti-frat or anti-independent (depending on which side you exist on). And I can't say for sure that there isn't racism/sexism/etc. within any individual organization that does buggy, but any of those issues are an organizational one, not a sweepstakes one.
Members of Spirit might be the best to answer the racism questions, since (I would assume) they would be most likely to be affected. Though their history as one of the dominant teams in the 1980s, and having been involved in sweepstakes for 30 years, indicates to me that there hasn't really been an issue, at least since the 80s.
I'll echo what Elmo said, in that I think most people who do buggy don't see things as racial; they see things as race-ial (Thank you, thank you, I'll be here all week).