Putting Rommel in control of 6th Army wouldn't have made a difference. The nature of the fighting was not suited to his style. The joke about him being a trickster VS a logistics wizard is actually somewhat accurate. 
However, if you'd put Rommel in some of the upper echelon staff of Army Group South during the 1942 breakout, things could have been very different. I forget the specifics, but the staff of AGS managed to clog the offensive over the Dnieper when it wasn't necassary (forces could have been better used elsewhere), and a couple weeks were lost with those forces... forces that could have been driving on Stalingrad. Had they been re-directed, then Stalingrad would have been captured with no resistance. Instead the Soviets managed to put up a defense after their armies were destroyed in the Don river bend.
However, if you'd put Rommel in some of the upper echelon staff of Army Group South during the 1942 breakout, things could have been very different. I forget the specifics, but the staff of AGS managed to clog the offensive over the Dnieper when it wasn't necassary (forces could have been better used elsewhere), and a couple weeks were lost with those forces... forces that could have been driving on Stalingrad. Had they been re-directed, then Stalingrad would have been captured with no resistance. Instead the Soviets managed to put up a defense after their armies were destroyed in the Don river bend.