Recently I've stayed at Protea Hotel Centurion and while my Marriott Rewards status seems to be recognised there are no points collected. After I contacted Marriott Rewards program support it seems that some Protea Hotels (even though they are listed on Marriott website) they do not participate on Marriott Rewards Program. One of them is the Protea Hotel Centurion at Pretoria, Johannesburg. So keep that in mind before booking that hotel.
Furthermore if you ever have to stay there avoid booking room 136. It's above the kitchen and there is an awful noise coming from the air condition of the kitchen. I had to change room in the middle of the night. Prefer always rooms on hight floors.