I don’t know if Dartmouth has the same thing, but Harvard has a page somewhere in which average SAT is given for students of various ethnicities. Native American accepted students had average SATs of about ~2000 - while this suggests a significant admissions advantage, keep in mind that these students may receive that advantage because of very difficult socioeconomic backgrounds. If your family is wealthier/middle-class, your ethnicity will still be a “hook,” but it may not be quite that big an advantage.