Most blues musicians use that style where they use their guitar to respond to the vocal lines of the music. I can't think of any blues off the top of my head that uses two vocalists using this... I'm sure their are literally thousands of bootleg collaborations of this sort of thing happening... but it's rare that a blues song is recorded with more than one vocalist.
I've pimped out Joe Bonamassa so much on this site I should be getting royalties from him.... but he blends a bit of a delta throw back blues style in his stuff quite often. A GREAT track to hear call and response on guitar by him is my all time favorite blues song "Blues Deluxe" by Joe Bonamassa...
Check this vid of him playing in Vegas with a 13 year old harmonica player from my hometown named LD Miller.... Him and LD do some call and response back and forth from guitar to harmonica that is pretty cool...
LD is also on JoBo's track "Your Funeral, My Trial" on his newest album...
http://www.youtube.com/watch?v=8gDCRY_UvZk