With that 6th run, there's almost no chance that the game going to extras would screw Team USA over. [in principle, a 7-6 Mexico win in the 15th inning or something would still eliminate USA, but the ghost runner makes such a result very unlikely]
DeRosa can breathe easy.
EDIT: Someone in the Reddit thread said they did the math, if Italy lost in the 13th or later 7-6, we'd be out. Every Italy run adds about 5 outs of extra insurance. But again, with the ghost runner, this coming into play is very, very unlikely. (probably <1 in 1000 or something)