For perspective:
Working at my course in the Drive, Pitch, and Putt contest for kids, there is a grid on the driving range to measure driving distance; the volunteers then radio back the distance. A girl hits a ball and we never see it at all, and assume that it has come nowhere close to the grid, which we radio back to the director. He tells us the ball went right at us, and we finally find it; it had gone over our heads, despite all three of us trying to watch it off the club. Her total distance was something like 230; we were standing at the far end of the grid and just never saw it. She was 12 years old, I believe.
Playing in a charity scramble, there was a Long Drive Tour guy on the tee of one of the par 5's. For a group contribution of $100, he would hit a tee shot that you could play as your tee shot, which we did. He told us he would hit balls until he had one that we would like, and that we wouldn't be able to follow the ball because of the speed off the club. On his third or fourth swing, he told us that he'd put one down the middle; none of the four of us had seen a single ball, and we were standing BEHIND him and watching carefully.
Spotters at a pro tournament are standing at a distance that is likely to be the landing area for most players, and then reacting to the motions from the guys with the paddles on the tee. I guarantee you that the don't see the golf ball until it lands on 99% of the shots, and nobody else could either. It is, after all, a golf ball in the sky coming down from over 100' and going FAST. You only notice those guys when somebody hits one into a weird place and they are sort of in the way. None of them can see the ball.