I'm not gonna wade through this thread because I could already tell from the first page that it was a shitstorm.
You're forgetting the UR in URM. But even in that sense, it doesn't really matter. Law schools have chosen to give boosts to a select group of ethnicities whom they consider to be underrepresented in law school and the legal profession. They don't make fine distinctions based on a particular state (even for schools in that state), but even then I would hazard that atheists are overrepresented in law school and the legal field (while still being a minority overall).
I would caution you against writing a DS about atheism. While it is possible to write one that comes off well, there is a much higher chance that it will come off as shit and annoy someone who reads. It's not worth risking that. If you want to write a DS about your low SES then go for it, you should do that.