John reports that Ellen Campbell says that the incident would not violate FERPA, the federal law protecting the confidentiality of student records:
It does not appear it would be a violation because these applicants were not yet "students" - the Department has long held that FERPA only protects the records of students as defined by FERPA. They are "students" if they are "in attendance." FERPA does protect records received from another school under the redisclosure provision - but applications or information provided by an applicant are not "education records" and those not protected.
John also reports that, according to a Wash Post story, Princeton was not just checking random students. Princeton checked on Bush's niece, who was admitted to Princeton and Yale.