Disney does do this. It is a special service for those with true medical needs / serious (as in life-threatening type) allergies - or at least that's the intent. If you check the DISability boards, they have the most information on the special department / phone number you call to arrange it. I wouldn't see any reason they wouldn't do it at a
DVC property and I'm pretty sure I've heard of people having it done in villas.
I believe it covers steam cleaning carpets, changing all the soft goods - and everything washed in non-allergenic cleaners, changing out air filters, etc. More than the housekeeping staff would normally do for a room changeover.
I think it's kept a bit on the down-low on the boards in general so not to encourage people who just want an extra-clean room to ask for it when it's not needed. One thing about it - if you get one, you can't change your room if there's an issue because they wouldn't have another room similarly cleaned and ready (so no "I don't like my view" or "I wanted bottom floor").
It is referred to as a VIP cleaning a lot of the time on the boards.
So don't ask for it unless you have a true need. And you never know, at a DVC resort, maybe they would charge you extra for it.