I don't think many people try to replace stress or depression with exercise.
People have varied ways to deal with their stress. Some of them can do exercises or do certain sports. Few people prefer to gather with family and take vacation somewhere. Meanwhile other people can choose playing games to release their stress. This includes playing gambling games, certain people can assume it as an entertainment to deal with stress.
If we talk about entertainment, gambling for a large number of gamblers is entertainment, but since it is a high-risk entertainment it can significantly affect the emotional background, which in principle can contribute to the deterioration of the state.
It will be a high-risk entertainment if we are too obsessed earning huge money from gambling. However, it will be a bit safe if we do gambling with small money for entertainment purposes. Sure, it becomes emotional if we spend too much money. But it won't effect too much if we only spend the money that we afford to lose.
Therefore, I also do not recommend gambling in stressful situations. It can lead to serious mental health problems. Play gambling when you are doing well and be sure to limit yourself when the situation requires it and then you will not have problems.
It depends on the problem that make you be stressed. It also depends on how you can deal with your attitude in gambling. If you are a typical of people who have good-self control, I think it won't be a problem to play. However if you are difficult to deal with your emotion, it is better to play when you have a calm mind.