I've worked at or (or received employment offers from) quite a few "name brand" Bay Area technology companies, have received recruitment email/etc. from many more, despite going to a university most haven't heard of.
Silicon Valley is much more meritocratic than Wall Street: if you can't pass a coding interview, the name on your diploma will not help you. A name on your diploma might make it easier to get interviews lined up as a student, but undergraduate research, open source contributions, referrals from other employees, are much more useful for that purpose.
That's not to say SV is without its own brand of homogeneity: ironically, whenever I am on Stanford campus, I am amazed at how much more diverse it is compared to the rest of Palo Alto.