Class rank from your high school is not considered by UC. However, GPA and ELC status are obviously correlated to class rank.
ELC status is determined by UC reranking a recent previous class at your high school by UC-recalculated GPA, then comparing your UC-recalculated GPA to the top 9% threshold of the reranked recent previous class (see http://admission.universityofcalifornia.edu/counselors/q-and-a/local/index.html#1 ). This should correlate fairly well to class rank, but may not match for some students (e.g. those at the top 9% margin, or those whose 9th grade course grades were much better or worse than their 10th-11th grade course grades).
Since the “rank” for ELC purposes is determined by comparing your UC-recalculated GPA to thresholds set by a recent previous class, there should be no incentive in the context of UC to cutthroat other students in your class to gain rank positions.