I would look at what each school asks for...for instance, some schools will explicitly state that if you've overcome some sort of obstacle due to your race, socioeconomic status, sexual preference, etc. then you should include that in a separate DS. However, some schools (can't remember which off the top of my head) define diversity more broadly and will say something like..."if you have special skills, interests, work experience, obstacles overcome, etc. that you think would add to our school's diversity, then please discuss those in a separate statement. blah blah"