Wile it is true that a bar is also a workplace, it is not required of bar employees to work there. They could just as easily get a job waiting tables/bartending/cooking, whatever, at a resturant where smoking is not allowed.
It's not like you didnt get the job there if the first place. People know if a place is going to allow smoking before they get the job.
If an establishment is a dedicated bar, and even mabye if its not. Smoking should be allowed.