Bellagio and its fountains sit on the Strip as a bright rectangle of water and lights. The night flight passes them in the neon run; the Red Rock return picks them up again coming back into town.
From a helicopter the fountains are part of the resort line, not a show you sit in front of. You see them from the air, then you are past them. Night is when the water and the lights read together.
See Bellagio from a helicopter over Las Vegas. Book the Las Vegas 12-Minute Helicopter Night Flight over the Strip.