So I am un-keying the bones so that I can move the T-pose to an A-pose model, and am wondering what bone_root is. bone_pelvis is located at 0,0,0 so I thought that was the one for centering the unit. Do I need to un-key this bone_root for rotating the bones for re-posing? And what is bone_root's legitimate purpose?

bone_root is for positioning the entire skeleton/unit in relation to your GroundDummy or dummyroot. bone_pelvis is an actual bone that you can use for animating the hips/legs, or for attaching things like kamas. I would un-key bone_root if I were you.