Yes, poking around SDN, I've read that OUWB is big on community service. I guess this should be indicated by the fact that their only required secondary essay specifically focuses on service!
EDIT: Now that I've thought about my essay some more, I realized that the two activities that I believe are "truly altruistic" that I have been involved in and was planning to write about I wrote about at length in my personal statement and in one of my Most Meaningful Experiences essays. Would it be OK to write about these experiences again, but perhaps from a different angle? I could write my medical volunteer activities, but I feel it's a bit disingenuous, as most premeds will have these similar clinical volunteer experiences.