Is there a way of querying a polygonal mesh at a given UV and translating where that UV location is to an xyz coordinate?
Not really.
Uv's don't map uniquely to 3d space tough 3d space maps uniquely to uv's (its not symmetric function). But if you know what specific polygon is in question then that is a another matter. (and if theres no overlap you could search for that polygon)
A simple hack I've used in the past is to attach a follicle to the mesh and let it do the converting for you, but that obviously only works if you're running unlimited.
nick