I have a theory on Unohana.
I believe that she has been in Gotei 13 since the very beginning and was there the last time the quincies attacked. I think she knows what their weaknesses are and can stop them. And that's what she is going to teach Zaraki!
It would be awesome to if she taught Ichigo, Rukia, Renji and the rest of Gotei 13 too!