Therein lies the confusion
My definition of "Bracers" is that of additional armour strapped on the forearm to protect the arm... i.e. Vambraces. Much in the same manner as a thick sleeve, albeit made of sterner stuff usually Hardened Leather or Plate
http://en.wikipedia.org/wiki/Vambrace
Given that these are generally can be purchased as add-ons, as opposed to an integral part of a suit they could in theory be worn by anyone regardless of AT. If my memory serves me right, these provide NO db bonuses but do negate certain criticals and already penalise missile use. If you fire a bow with any great regularity you will understand the problems associated with wearing baggy/bulky clothing on the arms which is why they do penalise the user.
So, in theory these could also be used to actively parry weapons with (in the same manner as a shield) , at least better than someone with no armour, no shield and without a melee weapon to hand.
Taking this a stage further, any other shield-like device should carry
at least the penalties that these already do as a static penalty if worn on the arm. In addition, because the RM round is a fairly lengthy affair, it may be possible to shift to a shield in the same round. If this is done then the penalty to missile fire can be determined by the activity used to change from bow to shield.
So generally I'd say that even Bucklers would seriously hamper the archer... but could be used with a large penalty to the missile attack. As others have mentioned, it's generally best just to dodge.