I asked this question before and, from the answers I've gotten, being a URM "helps" you a lot more than being a first generation college student. Note that I say "helps" as a purely statistical word and have not taken historical and institutional disadvantages into account.
Being a first generation college student is still a minor plus. Students without either parents having at least some college education who make it to the interview stage are (according to the answers I've gotten) not common and might even be a rarity.