MIT is the only top school I know of that specifies which Hispanics they treat as URMs. All the others seem to count South Americans as URMs (I know white students of SA descent who are invited to diversity admit weekends), but the extent to which any Hispanic is given preference is based on a variety of factors (SES, parents’ level of edu., etc). Students of PR and MA origin are the most sought-after by top colleges since we unfortunately have the lowest rates of college attendance compared to our population in the U.S.