Check out this nifty infographic illustrating diversity among Congressional staff:

http://nationaljournal.com/hill-people-who-are-they-and-where-did-they-come-from--20110616

To summarize, there's not much diversity. Republicans are generally less diverse than Democrats, but it's not such a big difference that Democrats can claim bragging rights.

The only really big difference between the two political parties is where their staffers live. Republican staffers live in Virginia, and Democratic staffers live in Washington, D.C.

I learned about this at http://www.americanprogress.org/issues/2011/06/atw_leger_capitol_hill.html