He is a pretty easy-going fellow with close relations to the base's drill sergeant, Arch Dornan and a similar, but not quite-so-extreme, intolerance for bullshit. He has a brother with stunted mental development serving in the Enclave Armed Forces.
If the Chosen One talks to the quartermaster wearing anything but advanced power armor, he will treat him as a new recruit. If he plays along, he will direct to the armory behind him, where the Chosen One can get a free suit of advanced power armor.
If one is wearing T-51b power armor, the quartermaster's dialogue will be slightly different. He will say "What the...? Oh, I can see why you are here." and tell the Chosen One to get a suit of advanced power armor.