Check the immd website
The Government of the Hong Kong Special Administrative Region - Immigration Department, specifically questions 47 - 50, although Q48 answers most things clearly:
Q48: My FDH has special permission to perform driving duties. Can he/she drive me to and from the office daily? A48: No. Special permission for an FDH to perform driving duties is given on the basis that the driving duties are incidental to and arising from any of the five broad categories of domestic duties, namely household chores, cooking, baby-sitting, child-minding and looking after aged persons in the household.
Special permission is required from immigration to allow a DH to drive in the first place!