Are the cockpit and crew rest area considered part of the cabin?
Speaking as an ex cabin crew with one of the world's largest airline. I can definitely say that the CRC is part of the cabin, as safety and security checks are completed by the crew as part of cabin checks. 

Flight deck if I'm not mistaken is not considered part of the cabin. However smoking is usually not allowed according to general aviation rules everywhere. Not even e-cigarettes are allowed. Why are e-cigs not allowed if they have no smoke you may ask? 

Reason is that many people might see someone using an e-cig and think that it's ok to smoke, hence lighting up a real one. This has happened before.

I've even had faulty no smoking lights on flights and passengers thinking that smoking in that specific area of the plane where the light is faulty is fine. 

When travelling people tend to pack so much stuff for their trips but leave the most vital thing behind - their brains!