Not infrequently buttock implants placed under the gluteus maximus do fill in the outer depression of the buttock/hip area. However this is on a case-by-case basis and requires a in person consultation with physical exam to confirm. For all my patients who are lean and have this depression, I recommend first undergoing buttock implants to enhance this area. From my experience approximately 80 to 90% of patients are satisfied with the results of this alone. For the rest, the only permanent option is hip implants because fat grafting in this area, especially in lean patients, will surely melt away.
Buttock implants do not go that far to the side. The 'hip dip' needs to be treated by fat injections.