We love renting points. We travel as a big group and we usually end up in 2 2-bedroom villas plus a couple of studios.
It's not at all against the rules, but there are some catches.
The first and biggest catch is that the DVC owner makes the reservation, even if you go through a broker. You request the reservation that you want, the owner makes that reservation with their points. The contract you sign is for that specific reservation, not for use of the points - those still belong to the owner. Does that make sense? Most contracts I've seen say no refunds, some may allow for a refund if the reservation can be rented to another travel party, but there's no guarantee of that.
The second biggest catch, imo, is that the owner also maintains the reservation. The reservation will appear under your name, but paid for with the points of the DVC owner. If you need magical express added, the owner has to do that. If you decide to add the dining plan, the owner has to do that, and they have to enter the payment for it. That means you either need to feel secure paying the owner directly and potentially giving the owner your credit card number to pay for expenses in addition to the room. I insist on paying with a credit card so I can make an appeal if the owner cancels, disappears, etc. And you have to trust the owner to log in and take care of those request in a timely manner.
The third catch is that to get larger villas or highly desirable rooms (like AKL studios), you need to book your room as close to the 11 month mark as possible. The closer to get to 7 months, the less likely you are to get the best value rooms. And because of #1 above, you have to be confident in your travel plans (or have a great travel insurance policy).
The fourth catch doesn't really matter to us - mousekeeping only comes every 4th day. We bring trash bags, coffee, and toiletries, so as long as we make a minimal effort in pick up after ourselves, we don't need mousekeeping. The 1 bedrooms and larger have a vacuum, washer, dryer, and dishwasher in the room. I'm not sure how things might feel now that they're potentially entering every room once a day and doing away with Do Not Disturb, but in the past we have enjoyed the privacy of no mousekeeping.
Some rooms and locations fill up very fast. I wouldn't wait to the 6th month mark to get a studio at AKL, they fill up fast! Since we travel as a big group, we always request reservations right at the 11 month mark to ensure everyone gets a room they really want.
The rest of the Disney on-site perks are the same. You get the same dining and FP windows, same EMH, same transportation, etc.