Set it Offffffffffffffffffff
I believe that the role of the white cop plays on both white guilt and an attempt to possibly place the view in identifying him. The white viewer possibly doesn't understand what these black ladies are doing. We know it is wrong that they are knocking over these banks, but we also think we know why they are doing it. The white cop allows for some escape and placating white guilt. In Thelma and Louise, this is much more simple in that the cop isn't coded in race, but in the feminine.
The landscapes in the two films are drastically different. One is urban and one is rural. One is constrained by the city, the people, the urban life, and one is set free in the wide open spaces, the lack of interference, the extreme extent of mobility. The only shot we even see in Set it Off that can resemble Thelma and Louise is the shot from the helicopter at the end when the women are being chased. Even then, this shot shows how they are constrained to the highway, being directed/channeled, to their end.