Still a no. Let's say they are responsible gamblers, but the urge will remain, and that single, minimal spark could ruin it all. He may use the funds that are meant for the people or for projects and infrastructures, which is why they are not allowed to gamble.
Then, it's called public service for a reason. To serve the public. To be a leader. To be a person that they will look up to. If they are gambling, then it wouldn't fit the criteria as a public servant. Actually, that is the one missing criterion in most of the politicians now. They want the position for power and gains, and not to serve.