SF: Sync data between SAP and SSFF

Hi Team,

   We are in the process of implementing employee profile, and have a couple of questions regarding the interface:

  1) for the User ID field, SAP recommends using central person ID or the external person. Since we don't use global employment and will not use it; would be ok if we use SAP employee number directly here (PERNR)?

  2) For the manager field,  we are going to use the "reporting structure" option. How does it react when for the org. unit of the employee there is no chief? (I'd expect it goes up and retrieve the higher chief, but not sure how it will actually work).

Thank you very much!