Cindy -
That's a difficult question to answer. I would guess it may have happened at one time or another since 1971, but unless you were at check-in when that "one too many" family arrived, you'd never know. I would think that if it did happen, Disney would graciously offer the family a room in one of the other resorts and give them some other compensations for their inconvenience. My only basis for stating that is...when we were evacuated from FtW in 2001 due to a tropical storm, they put us up at the Riverside Resort and gave us a voucher for $50 per person for meals at the food court.
From time to time I see motor homes in the 2000 loop and wonder why. My curiosity got the best of me one trip and I went to the front desk to ask why, and if we could book a partial hook up site for our 32' mh. Manager Jason told me that you really should not do that as those sites aren't set up for MH's. (Duh, if that's so, why do they have 30amp & 50amp service? They are just lacking sewer hook up's.) He would not give me a straight answer as to why you see MH's there - but just skirted the issue. One of these days I might just get brassy enough to book a partial hook-up site and hope for the best. I don't think most of the CM's at the front desk know the difference anymore. If we just go for a 3 day weekend, we can get by without sewer and just dump our tanks when we get home - where we have a sewer connection for the MH.