The definitions in MM7 all refer to melée weapons, and there is no mention in the Unarmed skill definition of defining feet and empty hands as weapons. (I've not actually checked, but MM9 may be different.)
At GM level, the Unarmed skill gives a chance to evade an incoming attack equal to skill level, and so in effect adds to armour class, but there's no mention here either of any benefits that Armsmaster might give.
If you have a character editor for MM7, you could find out. Try giving your unarmed character, say, 50 levels in Armsmaster, and see if it makes any difference to his to-hit ability.