HelloCustomerand welcome back to JustAnswer.
If the police were not called at the time, the only possible way that a police report
could exist is if the server went to the local police department after the fact and filed what is called a counter report (written report prepared by the citizen and filed with the PD). It is quite common for police departments to simply take such reports and file them without further action.
If your friend wants to be absolutely certain whether or not such a report was submitted, he can go to the police agency with jurisdiction over the location of the restaurant (city PD or county sheriff if in unincorporated territory) and ask if such a report was filed.
Even if it was submitted and filed, however, it is extraordinarily unlikely that even a top secret clearance check would find this report, because they are not entered into any statewide or national criminal
information data base. Not even the most rigorous background check goes to the point of requesting reports directly from every police agency in the country (or state), other than perhaps those where the applicant lives and/or works.
Another thought -- does the server even know your friend's name? If not, then it's a 100% certainty that no one would ever find any counter report that may have been filed.
By the way, there is no law against having a verbal altercation ... I can't imagine that anyone participating in a security background check would care about such an event, even if it was discovered.
Thanks for asking your question here on JustAnswer. If you have any other questions about this situation, please let me know.