By day, Hockney works as an auto mechanic—but he dabbles in crime on the down-low, with special expertise in explosives. As a person, he seems a little cocky. When the cops interrogate him, he makes nothing but wise-guy comments. They say they can place him in Queens on the night of the hi-jacking, to which Hockney sardonically responds,
"I live in Queens."
In the scene where he and the other four suspects are getting to know each other in the jail, Hockney helps wring info out of the guys, asking about Keaton's lawyer girlfriend, and about who "the gimp" is—meaning Verbal. Then, Verbal has to explain his identity.
So, he's helping feed us—the audience—a little more background, giving us the lay of the land.
Hockney participates in the emerald-stealing job, and goes to L.A. with the other "usual suspects" to fence the goods to Redfoot. He's present for all their jobs, but is not necessarily radiating his character, aside from making the occasional wisecrack.
In the end, he uses his explosives ability to help attack the boat containing the Argentinean gangsters. When he finds the van full of cash—which is going to be used to pay for Arturo Marquez—he experiences a brief moment of joy…before Keyser Söze shoots and kills him.