According to the following, USC considers legacy, aka “Relation with Alumnus” in admissions, but it doesn’t rate as “Very Important” or “Important”.
http://www.collegedata.com/cs/data/college/college_pg02_tmpl.jhtml?schoolId=1138
BTW - back when I was going to grad school in the late 80s, I remember someone in administration saying that for USC’s IE graduate program, you were admitted if you were in the top 50% of your undergraduate class. Most of the people I went to grad school with were fairly intelligent, but there was one guy - I don’t know how he graduated from high school. He somehow got his Masters, though.