I think giving credit to Rondo for Pierce's success is a bit far fetched, but KG certainly benefited (offensively) by playing with Rondo.
Pierce and Rondo had a complicated on-the-court relationship. Paul always wanted the ball in his hands more but was always a more efficient scorer when he didn't control the ball as much because the defense couldn't load up against him so easily. The two most efficient scoring seasons of his career (by a decent margin) came during seasons where Rondo was controlling the ball much more than him.
By the same token, they came in years in which you had players like Ray Allen and Kevin Garnett drawing a lot of attention themselves (to go along with Rondo of course)... so I just don't buy the notion that playing alongside Rondo somehow extended their usefulness or something along those lines.
A point of fact, Pierce had his most efficient months last season when Rondo was out. Many things contributed towards it certainly, particularly chemistry with the rest of the roster finally coming together, but there's that.