Even if the hobby turns addictive, it still doesn't stop the fact that it's a hobby, it only stops been a hobby when we no longer do it for leisure or fun but for the sole purpose of making money, at that point it's no longer a hobby but an extra job for an extra income, also known as a job on the side. Even with an addictive habit, a hobby remains one only that at they point, it may be gradually turning into a harmful practice that may have some negative effects on the gambler and in the long run becomes a problem for those who are around him too aswell.
When making gambling as a hobby there is a possibility that it can become addictive, you can even say it is certain to happen, the risk is that our lives will be destroyed, moreover, gambling has its own charm that can make players forget about themselves. Making gambling a hobby in my opinion is better not, the same as making a side income which in my opinion is just as unclear, of course, even that allows it to be addictive as you said and with addiction it is certainly not an addiction that leads to positive things.
Addiction that can make us trapped allows it to have a negative effect in the long run, because gambling addiction is something that can make finances a mess, the focus of money will only be used on gambling and it is possible to ignore other things such as basic needs that should be considered more. This is something that must be considered not to make gambling a hobby because it can be disastrous.