When Vance checked his firearm and showed that the magazine was empty of rounds, you see that the pistol was cocked and the slide forward. This indicates that there was one round left in the chamber because if the firearm had of been completely out of ammo then the slide would have been locked to the rear, so Vance could have used it, instead of a pipe, to stop the bad guy.
Vance's hotel room has a wine rack. Even the most expensive hotels don't do that.
Everyone (NCIS and the police) seems very blasé about the fact that Vance pummeled an intruder to death with his bare fists. Granted, the man had a gun but it seems excessive. Vance would certainly not be allowed to leave the country (his trip to Berlin) until the matter had been fully investigated.
It seems odd that the intruders take turns to fight Vance in regulation boxing style, especially since at least one of them has a gun. It seems merely a way for Vance to show his old boxing skills.