Woz never worked for Atari.
He built the first prototype for the game that became Breakout. At the
time, Bushnell would pay a bonus based on how few chips you could use
for building a game. Woz used HP custom ICs, which were unavalable to
the outside world to do it, so it had to be redesigned to take them
out to get the game into production.
Jobs was the Atari tech on the project (and was the one that got the
bonus, which he never told Woz about..)
This info was told to me by the VP of Engineering of Atari at the
time this all happened.
That's correct, Woz never worked for Atari - though he would hang out in
coin-op a lot at night with Jobs. I wrote an article about the
Apple/Atari connection 3 years ago that covers this topic as well as Jobs'
overall "career" there:
http://www.classicgaming.com/features/articles/atariapple/
Marty