Yes, gravity would pull the two metal balls together, even if they were placed 1,000,000 light years apart in an empty universe. Gravity is a fundamental force of nature that attracts objects with mass towards each other. The strength of the gravitational force between two objects is determined by their masses and the distance between them.
In the scenario you described, the two metal balls have mass, and therefore they would exert a gravitational force on each other. The force of gravity between two objects is inversely proportional to the square of the distance between them. This means that as the distance between the balls decreases, the gravitational force between them increases.
However, it's important to note that in the context of your question, the information about the universe being empty and the balls being the only objects present is somewhat contradictory. In reality, the universe is not empty, and there are numerous other massive objects such as stars, galaxies, and clusters of galaxies that can affect the gravitational interactions between objects. But if we consider an isolated scenario with only the two metal balls, they would indeed experience a gravitational attraction and be pulled towards each other.