Sarah -- Just to explain some background.
Foreign domestic helpers (FDH) -- mostly Filipinas if you want an English speaker -- have to be hired on a full-time contract. That means that you are responsible for their room, board, health insurance, etc., as well as a salary that is a little under HK $4,000 (US $500) a month.
Some people, like myself, will hire a Filipina "amah" (as we call them here) and then pay extra for her to live outside the home. As Carang said above, this is technically not allowed in the contract, but many people do it anyway. I know dozens of families -- both local and expat -- who do this. There's another thread around here that goes into those pros and cons. In a decade here, I've never heard of anyone being caught or punished for it. I think Immigration only gets involved if there is a case of abuse. But, again, there is a small risk.
Technically, FDH also cannot do outside part-time work, but most of them do. In my office of 20-30 expats, I think all of them use a part-time Filipina helper, who is usually paid HK 60-65 an hour (US $7.50- $8).
My husband works long hours and I work 3 days in an office, 2 days at home, where I need quiet and privacy. (I think we might do similar work). We are expecting our first child in a few months, and expecting our first "amah" in a few weeks. Like I said, we will pay extra for her to have her own accommodation. We also don't want her to squeeze into a tiny "helper's room" and be around us 24-hours.
We chose to have a full-time because of the impending birth, and because I will be returning to work several months after the baby is born. Our amah will mostly work as a nanny.
But before this, we were perfectly happy with a part-time lady who came once a week just to do the heavy lifting, like the floors and bathrooms. Otherwise, we did all our own groceries, cooking, laundry, etc., and were just fine.
Carang's reference to a "local person" means a Chinese person, usually a woman from a poor province of Mainland China. I've had some limited experience with local cleaners, and they were not good. They are more expensive than the Filipinas and, in my opinion, less careful, too chatty and can be a bit unprofessional. This is not meant to be a racist statement, as I'm Chinese myself. But there is a cultural difference. Also, the "local" or Chinese helpers will probably not speak English. This is not an issue for me, but it might be for you.