We reserved a GV for next March. We were told that the only GVs that have wheelchair access (ie, in the buildings with elevators or entry from ground floor) are the fully wheelchair accessible, handicapped units. Those are guarantee if you request it as the wheelchair accessible unit, because they are limited number and they have to block one to reserve for you. They do say that only requests for handicapped room are guaranteed; requests for medical reasons are not, but are usually not a problem to get for other rooms because there are a lot that fit the requirement of "first floor entry". In the case of the GVs, since there are so few of them, even if you don't want a fully accessible one, reserving an actual handicapped accessible one is the only way to ensure getting one that a wheelchair can roll into.
Usually having something as a medical request works, because they fill those before general requests. (If they are totally using room ready, though, that might change). But, in your case, you need to actually reserve a wheelchair accessible, handicapped room. Otherwise you could get there and find that all the ones you can use are already reserved.
From what I have read, the first floor of the villa is all that is accessible, even if the building has an elevator (some people were speculating that there might be a second entrance to the villa on a higher floor in the building).
Sorry this is kind of rambling, but I'm trying to write it as I get ready for work.