I'm pretty sure JHU only has two slots for fiction, and presumably five for poetry, but I can't verify that. I'm not even sure if they've made decisions on acceptances, though I'm guessing they have if people are getting letters now.
Regarding cultural diversity-- it's non-existent in the faculty. In poetry Mary Jo Salter was hired this past year but before that it was four white men. In fiction, it's all white, though it is two men and two women, and Alice McDermott alone makes this program worthwhile.
As far as student representation, two of the ten fiction students this year are woman, and one is Indian (the only non-white person in fiction), though in other years I've been told that women outnumbered men, so I think that's just the way the cards fell this year. There's also one Deaf person (me), and that's an aspect of cultural diversity as well. Two writers of color in poetry, and an even balance of men and women.
ZZ Packer and Louise Erdrich both got degrees here, so there are some big names. One thing is evident-- cultural diversity does not seem to be a factor at all in the application process. I know that the writing sample, as anywhere, is the most important thing, but I think that a good workshop benefits from a diverse range of voices. That being said, we have a great group in fiction.

btw, what's your state school in the midwest? I'm from Iowa City-- went to the U of Iowa. Basically another nameless state school, unless we're talking writing.