I don't think you should hide anything from your spouse, and that includes gambling too. Gambling addiction is bad on its own, then hiding it from your partner is a betrayal. Gambling has to do with your finance, so it's very important you share it with your partner, so you both can even make a budget for it, so it does not affect your finances.
Hiding your gambling habit from your partner could lead to divorce, when they find out that you have been hiding it from them. They will definitely feel betrayed and it's really going to affect their trust for you, and when trust is broken in a relationship, it's might lead to a divorce.
Sometimes we need to keep Somethings to ourselves regardless of the level of trust, i know that my spouse knows i gamble, but she also know that i have been gambling as responsible as i can, and she doesn't have anything against me so regardless if i tell her or not, she will definitely not feel disappointed if she discovered that i gamble.
I believe the most important distinction here is that the household is or is not being affected by gambling. When it is just a little hobby and the boundaries are kept strict, most of the partners will not really mind especially when there is already trust in the relationships. However, when a person begins to conceal it, the secrecy itself may become bigger than the gambling. I have a friend who occasionally gambled and his wife was okay with it but the second he started to hide losses the trust was more hurt than the lost money. Transparency will therefore both save the relationship and finances in the end.