If Giteau was eligible I'd have him in the squad in place of a third halfback, mostly for his versatility/experience, but he wouldn't make my starting side.
Drew Mitchell would be no where near the my squad. If you're an outside back you need to prove you can match it in Super Rugby with the heavyweights. He hasn't done that for years.
And do you really think Gits would make himself available for a role as 3rd half/utility dirt tracker?