In fact, you cannot treat gambling as passive income in any sense. If you do not gamble, you won't have any chance for income on the other if you bet, you have no chance of winning you can make loss as well. However if you are staking on any casino site it would be your pass income otherwise we cannot adjust it with passive income.
If you can come to such a conclusion, you know what to do with gambling. Gambling is just a tool to help us enjoy our free time and not to be used as passive income because it is very difficult to do unless you can own your own casino. Gambling can indeed provide income, especially for those who can win many times but please remember that those who often win will also experience defeat. For that, it is better to use gambling as a way to enjoy our time and nothing more.