The answer to this question is somewhat complicated, but it can be broken down into two main points. First, it is generally not possible for a roulette dealer to control the ball in any way.
Second, even if they could, it would not make much of a difference.
The first point is relatively simple. Roulette balls are made of metal and are weighted to ensure that they will spin around the wheel in a predictable manner.
The roulette wheel itself is also made of metal, so any force applied to the ball (whether by the dealer or another player) will cause it to move erratically and potentially impact other balls.
There have been cases in which dealers have been accused of influencing the ball, but these allegations have always been proven to be false. In fact, it is illegal for a roulette dealer to influence the ball in any way.
If caught doing so, they could face prosecution and/or fines.
The second point is more complicated, but ultimately remains unchanged by whether or not a dealer can control the ball. As mentioned earlier, the roulette wheel itself is made of metal and is therefore resistant to most forms of force.
Even if a dealer were able to apply enough force to the ball so that it impacted other balls in an undesirable way, this would only happen very rarely – and even then it would only be because of random chance.
