Such arrangements in and of themselves are not harmful. Some districts implement plans whereby some of the students are transported to other districts in order to take advantege of educational opportunities in those districts. So, in some cases, the arrangements are actually quite helpful from an educational perspective. The real issue for you is what is in your children's best interest, and you are in the best position to figure that out. Why are the children being transported out of district? Do they require a resource that your district does not have. I'm afraid you won't find research evidence to buttress your opposition because generalities can't be drawn about this issue. Keep your eye on the goal - i.e., selecting the best program(s) for your children.
Anything peer-reviewed would be even better