They do not have dedicated rooms, but they can do a special cleaning of the room depending on the person's specific needs [eg using fragrance-free cleaners, fragrance-free detergent and extra rinse for linens and towels, etc].
The place to contact is Disney's Disability Services:
https://disneyworld.disney.go.com/en_CA/guest-services/guests-with-disabilities/
Disability Services at (407) 560-2547 or email
disability.services@disneyparks.com
If they are not exactly the right place they will refer you to the specific department who is.
If you search "Allergy Cleaning" or "VIP Cleaning" on the boards you will get more information. Also, posting in the Disabilities section of the boards may get you some additional information.
Also, depending on the person's specific allergies, give consideration to the room choice. For example, we have found we do much better in the rooms that have hardwood-like floors vs the ones with wall-to-wall carpeting. Fortunately for us, as Disney renovates their rooms they are moving towards the hardwood-style flooring
ETA: A few things to keep in mind:
When you make the request it is best to frame it exactly as you did... the guest has severe asthma and is very sensitive to many cleaning products, and are concerned about the products that are used, particularly with covid; you are therefore wondering if it is possible for the room to be cleaned with products that are not as likely to cause problems.... And then be prepared to explain what that means [e.g. no fragrances; no bleach; if there are certain products that are a specific known problem, etc].
Also, know that if they do the special cleaning you are pretty much stuck with the room, as the cleaning can take hours to do. So, if you don't like the location or view of the room you are assigned, you can't get a new room. Also, they room probably won't be ready early, and may even be ready later than normal checkin, again due to the time it takes to clean it, so be prepared for that possibility.
Finally, if you do make a medical request for a room [which the allergy cleanings are], when you get to the resort and check in, **go to the front desk and verify the request is being implemented** even if you have 'direct to the room' checkin and would normally be able to bypass the front desk. For our last stay, in December 2019 [a split stay around a
DCL cruise, with both pre and post WDW hotel stays], there were communication errors between Disability Services and the hotels such that the hotels did not receive the request. Since we are Canadian we had to do actual checkin at the front desk anyway, **but if I had not specifically asked about the medical request* the hotel would not have known and it would not have been implemented. Even for our post stay, where the pre-stay hotel sent a new request directly to the post-stay hotel, there were communication problems. This can also be a problem if a well-meaning CM tries to give you a room location change [such as for a better location or to get you into a room earlier] or pixie-dust room upgrade not having read the reservation notes thoroughly to realize that the room you were assigned is getting the medical cleaning. So, advocate for yourself and proactively ASK to make sure the request was received and is being implemented *for the room you are being given*. And plan that if it has gone sideways it can take some time at the front desk to sort out -- for our December stay it was OVER AN HOUR at the front desk.