The only people who can provide the real details would probably be current OMFS residents at UCSF or someone whose been through the fellowship. My guess from reading about the position on the AAOMS site is that it focuses on treatment of Maxillofacial pathology and the subsequent reconstruction.
Just an aside but its probably a little early to be thinking about fellowships until your in about your third (4 yr tract) or fifth (6yr tract) of residency to give yourself a chance to know what types of surgery you enjoy doing.