I've never understood why people feel there has to be conflict. We only have one all-star gym in our area, and three of my current high school cheerleaders participate in all stars. I have an understanding with the all-star gym owner and the rule on both teams is that if there is a conflict, WE get to decide the priorities. We communicate regularly, and if it's my last practice leading up to Region, State, or UCA, then I get the girls. If it's their last practice leading up to a competition, they get the girls. In both cases, we generally work out some sort of compromise where we only lose the kids for 15-20 minutes a piece.
As far as injury...
We both place a high priority on safety in our programs, and perfection before progression. I've had more kids injured in high school gym class, than I have all star cheer.