Mike Ross should be the third tighthead. Cross isn't good, and if he got destroyed in that match throughout not just that one scrum. And has been all season as well, Edinburgh even conceded a penalty try to Munster IIRC. I don't see how he was that good off the bench for Scotland anyway.
Hamilton is indisciplined and exactly the kind of player I could see losing his cool and gifting penalties to Australia. Last year I remember he conceded like 5 penalties in a match against Italy, it's been a problem throughout his career. Not only is Hines a much better player with a more complete game with more handling/ball skills, Ian Evans is also a better player who is a more athletic useful big lump than Hamilton. Also the Top 14 final is just one match vs Barbarians, doesn't rule out for the entire tour. Out of interest, Hines actually turned down playing in the Top 14 final in 2009 to join the Lions tour and had his contract terminated by Perpignan as a result, that was why he joined Leinster in the first place.