They do not require SAT Subject Test Scores, but they are recommended for Engineering. From their website:
“Applicants to the Henry Samueli School of Engineering and Applied Science are strongly encouraged to take the following SAT Subject Tests: Math Level 2 and a science test (Biology E/M, Chemistry, or Physics) that is closely related to the applicant’s intended major.”
So, if you want to be a competitive candidate and you are applying to an Engineering major, you should take the Math Level 2 and 1 Science test and submit the scores, but if you are applying to another major they are not necessary.