rush

top tiers are more legacy based than "just being from the south".

top tiers = legacy based and some hometown based.
mid tiers = they look at your application and try to find fits. even if you are from a far out place like Vermont and one kid in a frat is from Vermont and you click with that kid, then that kid alone can get you into a mid tier pretty easy. (we try to keep our actives active, and if there's someone in his backyard then we'll bid him).
bottom tiers = they mostly just try to fit in spots.

tiers aren't so heavy based for frats as it is for sororitys.

i don't think top tiers applies to you. maybe if you click with a few guys you'll get mid tier, if not bottom tiers are fine. great guys. just don't have connections. for some reason people think of tiers like it's high school. there are a ton of preppy, good looking, jock types in bottom tiers. again, it's legacy based and home town based.

can't comment on the military thing. i'm sure all bros respect it. they are just worried about the time commitment if you'll have time with the boys while doing your duties. that and very few frat guys are military so they'll feel a bit disconnected to you since it's not a shared interest. But overall i don't think it'll hurt you much (if any).