A contract can be very useful to spell out the rental process and specify each party's obligations. How much the renter will pay and when, what documents the owner will supply and when, that sort of thing.
But, in order for a contract to be enforceable, that implies that someone has the power to enforce it. A
DVC rental is a private arrangement between two individuals. As PPs have said, Disney will absolutely not get involved if anything goes awry. The parties can go to small claims court, but that can become quite complicated if you're in two different states. So, really, there's no 'protection' provided by a contract, not in the legal sense.
If you're looking for an ironclad guarantee, as a renter or an owner, you won't find one. But, the very great majority of rental transactions go out without a hitch.