DHs are entitled to the day off on all statutory holidays (or an agreed substitute day), but are only entitled to be paid for them after they've completed 3 months of service. (This is the case for all employees, under the Employment Ordinance.)
So, if a DH has not yet worked for 3 months, then she should get the day off and technically an employer can deduct a day's pay - BUT it would seem rather mean and petty to do so. I think a lot of DHs just don't get stat hols off in their first 3 months, but they are supposed to.