Yes, SET contracts can be capacity controlled or last available room. Different companies will manage their relationship differently so a single "pat" answer may not apply. Some will even vary from property to property, especially those near major facilities. Some companies get a list of names of those using their negotiated rates. Massive violations may result in tighter rules in the next contract.

I am retired and still use the company SET rate. I make it clear when checking in I am retired and there has never been an issue. Someday I'm going to run into someone that will make it an issue. When that happens, I will take appropriate action (always know what alternatives are in the area).