I wouldn't say that there is NO risk (an owner could not pay their MFs and DVC could cancel all their reservations). But your money is safe if something like that happens. The brokers guarantee that you will either have a reservation or you get a full refund but they cannot guarantee that they can acquire another reservation for you.
Suffice it to say that the brokers are a pretty safe route to take. But a private rental thru the Rent/Trade Board here can be pretty safe if you do your due diligence. There are a number of owners who post there who are active members of the disboards.