The legality of a bartender gambling in the bar is contextually dependent on local laws and regulations governing gambling and alcohol service. In many jurisdictions, there are no specific laws that prohibit bartenders from gambling while they are on the premises of the bar, as long as they are of legal gambling age and the bar is not a casino that has stricter rules regarding employee conduct.
It's important to distinguish that while a bartender may be allowed to gamble, they must be mindful of not interrupting their duties or engaging in any behavior that could negatively affect the bar's operations. Additionally, some establishments may have their own internal policies regarding gambling among employees, which should also be respected.
Thus, in areas where there are no legal prohibitions on bartenders gambling in the bar, it can be considered legal. This is why the first option is the most suitable answer.