Depends on the ship. Gators (LPDs and LSDs) have a Warrant for a DCA and a 2nd Tour Divo JG-type as ADCA. The way my buddies explained it, they did all of the paperwork and boring DivO stuff while DCA stood EOOW, drank coffee, and stole snacks from the Chiefs' Mess.
Small Boys have a 2nd Tour DCA and usually an over-abundance of ensigns so usually an ensign gets sent to Repair Division as R-DIVO so he can do all of the paperwork and normal Divo stuff while DCA stands EOOW, runs DC drills, and gets yelled at by XO and CHENG.