To answer the original question, I understand it's betterto say one's ethnicity than not to. I know a student who's now left Boalt but who was on the adcom, and who said that they preferred to have race and income fully filled in, even if it appeared the applicant is white and financially/socially privileged. According to her, at least this way the person was coming out with who they were and weren't hiding, which is seen as more suspect in her opinion.
I thought it was interesting at the time.