Pettine has done a pretty good job as a defensive coordinator as well as one that side of the ball while being head coach therefore I'm actually fine with the Packers hiring him as DC.
While the combined record of his teams isn't impressive at 50-62 (.446) the quarterbacks he had to work with should definitely be considered:
Mark Sanchez, Greg McElroy, Tim Tebow, EJ Manuel, Thad Lewis, Jeff Tuel, Brian Hoyer, Johnny Manziel, Connor Shaw, Josh McCown and Austin Davis
I'm optimistic he will be capable of fielding a defense good enough to be successful with Rodgers throwing the ball.