AoA vanes actually do work on different principles than pitot probes. The newer, fancy-schmancy ones use a whole bunch of tiny ports, each measuring pressure at different angles, and a computer interprets the results to give AoA. On older planes (including the one I have the most experience in), it's literally a vane, as in "weather vane:" it rotates into the direction of the relative airflow, so whatever angle it is at relative to horizontal is the AoA.
Even if the AoA system did work on the same principle, the more important point is that it's a separate system, meaning that a failure in the pitot-static system would not cause a failure in the stall warning system.
EDIT: from the picture you linked, the AoA vanes on an A-330 are of the type I'm more accustomed to: literal vanes that rotate into the airflow.
AFAIK stall warning system uses AoA vanes, located on the nose close to static system pitots. Completely different system? Yes. Same working principle? Yes.
http://msquair.files.wordpress.com/2010/03/aoa-rs-probes-a33...