If you're not in the US, you are not expected to go on-campus for a self-initiated interview (though it is a major indication of your interest if you do). If you decline the self-initiated interview, and Tuck likes your written application, the admissions committee will send you an interview request, which you can do over the phone. I don't believe Tuck admits any applicants without interviewing them (whether self-initiated or Tuck-initiated).