Can a bartender take a shot?

Not in Arizona

TITLE 4, CHAPTER 3 4-244. Unlawful acts 12. For a licensee, when engaged in waiting on or serving customers, to consume spirituous liquor or for a licensee or on-duty employee to be on or about the licensed premises while in an intoxicated or disorderly condition. Eye Spy Spotter Services

Depends on the rules of the bar. But if you're bartending in Newark you better be able to take at least one "shot".