With very few exceptions, students with decent GPA's and good work ethic are not at a disadvantage no matter which school they come from. There are great residency programs that attract top students from all 9 schools, and there are programs close to schools that tend to stick to their own. I would assume that residents who were upperclassmen to current students may help said students attain a residency spot, or get preference from a director who lectures at the school. If you really want a specific program then visit, rotate, interview, and see what happens.