As noted above, the only portion of breakage income that goes to offset dues is the amount that equals a maximum of 2.5% of the operating budget. After that, a portion goes to offset costs of operating the Disney entity that is MS. Anything left goes essentially to
DVC for its own use.
By law, the developer which owns units can choose to either pay dues for the units or do the noted guarantee of the annual estimated operating budget which means that if costs exceed the budget it covers the excess and doesn't charge a special assessment for excess perating costs. DVC has chosen annually to go that route. (Note it still has to pay its share of property taxes.)
There is a mangement fee in each budget that is a set percentage (about 12% of the operating budget without the management fee) for which the percentage cannot change, but the total amount of the fee can obviously increase annually if the budget increases annually. That is, besides breakage income a second way management can essentially profit from DVC. However, there is an interplay of several provisions. The MS budget is covered by what might come back from breakage income, that management fee, a charge of $1per member annually for a reservation fee, and the $95 trading out fee charged, which fee is not part of the actual annual budget but is paid by those who trade. The combination of all those things most likely well exceeds (probably by a multiple, and some might believe, possibly incorrectly, by an order of magnitude) the actual cost of operating all of member services, with the result of a profit built into the program (perfectly legally one revealed in the offical documents). It is one reason why Disney looks at DVC so favorably -- it gets the sale amount and then profits continuously thereafter -- and one reason it is unlikely ever to consider torpedoing any resort like VB.
As to websites that just offer an arena where others can post offers to rent, they are unlikely to do anything. As to shutting down websites that the owner is using to promote his own rentals, you would be raising First Amendment Issues that likely prevent shutting down the site. They can of course act to prevent one from using any Disney trademark. They could pursue the owner for possible remedies for violating the commercial purpose restriction but would not be able to get an order shutting down the web-site based on that. If they did anything, it would likely be to find a way as noted above to cease taking ressies because the member is engaging in a commercial purpose.