Visible crew/equipment: When Robert De Niro goes to meet Joe Pesci in the desert, the whole crew is reflected on the side of the car.
Visible crew/equipment: In the scene where DeNiro is throwing Sharon Stone's character out of the house after overhearing her on the telephone, he drags her into the bedroom. Just before the scene cuts away, the camera appears in the mirror on the wall behind them.
Visible crew/equipment: When Ginger obtains the deposit box's key after having rushed to Ace's house and goes to the bank to open the deposit box, a boom mic can be seen reflected on the bank's glass door.
Answer: It's also possible that the "bosses" would be concerned that a rift between Nicky and Sam could bring public (police) attention to the criminal activities going on behind the scenes. These are, after all, two very egotistical individuals.