DeJesus is not the kind of player you "platoon." Further, while he would be a nice addition, the Reds don't need a player badly enough at that position to justify giving up what the Royals are more than likely to want.
If the Reds are to acquire a bat, with the intention of being a starter, shortstop is where they need to look. They stand to gain far more by way of improvement there than anywhere.