The trauma guys at my program are essentially already doing ACS. Here (reasonably-sized academically-affiliated Level-I trauma and tertiary referral center in a small city in the southeast) the trauma staff (currently consisting of 5 attendings) take general surgery call. When they are on call, they cover both trauma and our emergency general surgery services.
For rounding responsibilities they rotate: in a given week one is responsible for trauma floor rounds, one for critical care rounds, and one for EGS. Weekdays 8-5, the one responsible for critical care rounds is the one who takes all incoming trauma and EGS admits/consults. At night and weekends, it is whoever is on call.
I've seen other arrangements too, this is just the one I'm most familiar with. Grace Rozycki recent gave Grand Rounds here and detailed a lot of changes going on with ACS - its a developing field and some critical care fellowships are developing themselves to be "acute care fellowships," expanding to two years for this purpose.