Yes, the shower situation is true, and yes, some kids in the dorm might think it was prudish to vote against co-ed showering. So be it -- it's just a part of life at Oberlin that some people are going to be to the left of you and think that you're a tool of the patriarchy for: eating eggs/participating in biology experiments that use rats/wearing clothes that aren't hemp/etc. It's possible for a mainstream liberal student to find a niche at Oberlin, but you do have to get used to the fact that you will never be "progressive" enough to satisfy some segment of the population.
My recommendation: avoid that dorm. They still let you express a preference, don't they?