Hey there the_fella,
I believe that med schools are allowed to tailor how they are defining their local sense of urm and how to recruit a diverse class. For instance, in California, I believe certain schools look for Hmong and Vietnamese applicants to recruit (despite these folks often getting lumped into the broad 'asian' orm category by other schools). not sure if certain schools close to appalachians might also try to recruit from appalachians...worth calling their diversity offices and asking whether they do. similarly, some schools in rural places might try and recruit more rural folks.
Appalachian and first gen at college is covered by the economically disadvantaged category, which is another aamc-defined category that runs side-by-side with urm. amcas asks about parents and level of education, and might still have a box for describing ec dis status? if so, good to put appalachian identity in there, with what that means in terms of less likely to go to school etc and paint the picture.
i'm not sure of any schools that have lgbt as one of their categories for diversity. there's a story in an anthology called "what i learned in medical school: personal stories of young doctors" published 8 or so years ago, of a guy who hyped his lgbt status in personal essays about perseverence and overcoming and ECs within lgbt community and didn't check-box his economic disadvantage status, and wondered at one point whether he had done a disservice to his chances with that.