I actually spoke with MS and the manager of billing for Disney resorts. The information I received did not come from the valet or anyone at any valet kiosk.
To clarify, I only stay onsite at Disney, so I cannot speak from personal experience using valet when staying offsite. That said, I will elaborate on the information/instance that I referred to.
For the weekend, I used a cash reservation, not DVC points; the other 10 days I used DVC points. On the days of my cash reservations, I used valet, unknowing that anything would change. On the final day of my cash reservation, I noticed 2 charges for valet at DVC resorts (2 days). I called billing and inquired about the charge. I indicated that I was a DVC member and the resorts I used valet at are DVC resorts. The CM told me that as a member, I have the free valet option when staying on points. When not using points, there is a charge for valet.
I disagreed with the CM as it didn't make sense to me, and I was also told nothing about having to stay on points to get free valet. The CM directed me to the supervisor/manager on duty. The manager echoed the same thing the original CM had told me. That since I was not staying on points for those 2 days, the valet was not free, only free when using points. I then called MS to verify the information I was told, and was told the exact same thing by MS and the MS supervisor on duty.
There is no way the CM's at the valet stand verify the information when dropping off or picking up the vehicle. The only take the number and then let the billing system determine if it's free or if to charge it to the guests room.
Since I also think it makes no sense not to get free valet when staying offsite or with a cash ressie, I made sure to go through 4 different CM's/supervisors to get the information I posted as correct, to my knowledge and experience.
That said, there could be no way for the valet person to know if you were a DVC member staying on points or not when they give you the valet ticket. So, it seems to reason, that if you are staying offsite there would be no way for them to charge you for the valet service. Since I was staying onsite, it was quite easy for them to find me and charge the valet fee to my room.
There are 2 different opinions as to how and what is offered, and I am posting from what was told to me by 4 different CM's and what I have personally experienced. I believe that if you are a DVC member you should get free valet at any DVC resort, whether staying on points or not. I was also never told about any stipulation regarding staying on points, which is why I chose to valet when on a cash reservation, but apparently this is not the policy. I have not read this policy anywhere, but was told the information by no less than 4 different people in 2 different guest service call centers. Just my .02