That reminds me of an enlightening incident about identity and self-concept. I was with a group of about 15 Indians and Pakistani for a club meeting. The following discussion occurred:
"He's the Asian guy"
To which I could not help but comment: "But you're all Asian!"
And one replied: "No, no ... we're SOUTH Asian."
Now, for the URM question ... read the definitions. If none is presented on applications, it can be considered ambiguous, and you're allowed to read into it what a reasonable person would understand it to mean. I would venture that if you are American, and you're ethnic/national/religious/whatever criterion group is found in law schools in a smaller proportion than in the general population, you qualify as underrepresented.
And CANE is right ... diversity statement is a must