that truck is an 03-07.5 and im almost positive onstar was standard on some trim levels but not all. if its a W/T or similar trim (bare bones) then probably does not have it.
if the company or truck owner even knew the first thing about their vehicle they would have called onstar right after the police, infact many officers will ask if the vehicle has onstar, LoJack, or any other tracking device before they even put out an APB about it.
if you have no onstar or anything... i hate to say it but the truck was at some tweakers back yard or a chop shop before the police even filled out paper work.
Dachshunds could very well be substituted by ferrets, obviously.