Carters, Keath and Hill have obviously been around a bit, but something from them would be good. Carters and Keath definitely have some nice strokes, but Hill recently has built more of a reputation for defence.
Evan Gulbis is a bit of a prominent name in Melbourne cricket. He made a stack of hundreds in the last two seasons and can handle the T20s, but he's in the middle of a rough season at the moment and I'm not sure where he figures. He has taken a few wickets this season and tends to bat up the order, so perhaps he is there simply as someone who can cover a lot of gaps.
Salpietro on the other hand is probably there for his offbreaks and may start as a number 8, leaving Gulbis 12th man.