And I've heard that you had to be 1/8 or have tribal registry to be considered in California, back when we still had affirmative action. But my source is suspect.
The real question may be, does you native american heritage affect your life (except for purposes of admission)? Did it affect where you grew up, your education, your parents education, etc.? Does it affect people's perception of you? That's what is looked for when you claim URM status, but are not sure you actually qualify.