Yes and no.  While casino charges do go on your cabin account, only non-HAL issued OBC can be used for this purpose (thus, HAL issued OBC cannot be used).     Understand that during the course of your cruise, it might APPEAR that HAL OBC is being used for your casino charges, at the end of your cruise (usually the last day) the account will be adjusted and you will be billed for your casino charges (sometimes HAL drops the ball and misses this adjustment, but I would not count on it).