Yale reports statistics based on these “buckets” on their own website - https://www.yale.edu/about-yale/yale-facts (you have to scroll down to the section labelled “University-wide Enrollments by Ethnicity (% of non-international enrollment)” and click to expand it)

You think, if Yale publishes these statistics on their website, that Yale’s admissions officers aren’t thinking about them during the admissions process?

You should look closer at average test scores of admitted students by more fine grained ethnic groups. My high school discriminated by particular ethnic groups: Chinese, Japanese, Indian, Hispanic, etc...

Are those figures – i.e. test scores of admitted students broken down by fine-grained ethnic groups – publicly available for Yale? (Or any other similarly prestigious US university?)

Pacific Islander vs Asian isn't "fine-grained". They are two distinct "buckets" in the US government's standard racial classification system, to which I linked earlier [1]. It is just that the "Native Hawaiian or Other Pacific Islander" bucket sometimes gets its name abbreviated to "Pacific Islanders". "Pacific Islander" is a collective term referring to the indigenous peoples of the islands of the Pacific Ocean, which peoples are divided into three main ethnolinguistic super-groups – Polynesians, Micronesians and Melanesians – and Native Hawaiians are a Polynesian people. New Zealand's Maori are another Polynesian people.

Prior to 1997, the US government had a single bucket, "Asian or Pacific Islander". Since 1997, they've been split into two separate buckets (although it took some time for the bureaucracy to fully adopt the new grouping – the 2000 census still used the old classification, but the 2010 census adopted the new one.)

[1] https://www.census.gov/topics/population/race/about.html

The lawsuit asserts that they discriminate on the basis of both race AND national origin.