yes, in an extended dive, when the tank is nearly empty, the clunk will draw air. In the real world that seldom happens, because you are generally not in a dive long enough to kill the engine. If some air gets drawn into the line, it will not always kill the engine. And when you are pointed down, the throttle is usually at idle, so only a miniscule amount of fuel is being used.
Also, when you first point the plane down, the fuel does not immediately drop to the front. Picture you drop the plane (in a vacuum) and the plane rotates to the nose down position. The fuel drops at the same rate as the plane and stays where it is. But in real air, the plane does not continue to accelerate downward but is slowed by the air. And the fuel does fall to the front of the tank.