My contractor wants to vent our bathroom exhaust fan by connecting tubing to our attic turbine vent (aka whirly bird) to exhaust it to the outside instead of plumbing it to the outside through the roof. Is this up to CA codes? This seems like a short cut.
Your contractor is lazy. The best solution is through the wall (though not near an eave), but if that is not possible, a dedicated vent in the ceiling is necessary.
If there is no wind, dumping the hot moisture-laden air into the whirlybird will just put it back into the attic.