It depends.If he is a pussy all house and church and is afraid of all what people might perceive as unhealthy activities it is better to not tell him that you are involved in such activities.In case he is a real man then even if you tell him I don't think he will make a big mess about it and most likely accept what you have been doing,maybe he will start giving some advices and monitor you more than before but overall I don't think it will be a big problem for him.In the end as you see depend on the type of guy your husband is.
Even if she doesn't tell him, he will know about this secret at some point. It's impossible to hide a gambling routine, because it directly interferes on the financial life of the couple. The husband will notice there is money missing, so he will ask the wife where she has been spending it. If she lies, it will get even worse, as the husband will become highly suspicious of her and will start looking for left tracks of the money. He just need to check bank account's history to see deposits made at casino platforms.
If she decided to lie, then I fear it's the end of the marriage, because he won't trust her anymore, doesn't matter the situation. And without trust, no marriages can exist, at least in a true way, although there are people who decide to remain together solely for formal reasons, to not disappoint the society or not be criticized by people around.
To tell the truth is the best alternative, despite the consequences.