Provisoning API only handles username, firstname and lastname, all other contact fields for the user profile are set via the Profile API:
the API is very similar to the Shared Contacts API, the main difference being that User Profiles cannot be added or deleted, they simply exist for all your users.
Do note that there is no way to hide specific fields from users so if uploaded by the Profile API, the unique ID would be viewable by all users on the domain (unless the specific user is hidden from the directory via the control panel but that would hide the user completly).
Jay