Husband is getting chaptered out of the army, can he hire a lawyer? does it have to be a lawyer on post?

Long story but my husband is facing a chapter and I am worried it will be OTH or general resulting in loss of the GI bill, VA loan, VA benefits, etc. He is in a medical unit because he was injured while deployed and I feel he is being treated unfairly. Can he hire a civilian lawyer? Would a lawyer on base be beneficial or are they always on the army's side?