Michael Schoch, Answers questions on Noodle
Salesian High School describes its non-discrimination policy in the student/parent handbook. It states that it doesn't discriminate on the basis of "race, color, disability, or national and/or ethnic origin"; However, I couldn't find a passage anywhere that definitively said whether or not a non-Catholic student could attend.
To find out I recommend calling the school at (323) 261-7124. Best of luck!