With contract length (two years each) and money ($28 million for Hill, $26 million for Prado), being almost equal, it would make more sense for the D’backs to trade Hill. The option is there to move Didi Gregorius to second base with his experience playing there at Triple A Reno this year. Prado himself could man the until the end of the season. It would be more difficult to find a suitable replacement for Prado. Andy Marte is not viewed as a long term answer at the position. Jake Lamb, despite his 77 RBI’s is still at Double A Mobile.
The Snakes have already dealt three players in Brandon McCarthy, Joe Thatcher and Tony Campana. There is no rule that states they have to trade anyone else right now. The right time to make the next deal could be in the offseason.