Well I actually just called Marriott and was told there is no restriction for Protea hotels. She said that when booking (after confirming the award space is available for 7 nights) to call Marriott and they will attach the certificate to the stay. I haven't done the research yet to know if it represents good value vs just using points per night, but I love Cape Town and stayed at a Protea hotel in the Stellenbosch wine region - was upgraded to a two level staircase/fireplace suite for just 7,500 points per night.