All hotels in the U.S. are required to have a certain number (vs. total inventory) of (1) Handicap accessible rooms; (2) adjoining rooms; and (3) handicap accessible rooms that adjoin with another room. SO, in short, they all SHOULD have connecting rooms; but some still don't. Some places can get by with offering large suites (places like Homewood Suites come to mind) that meet ADA requirements as their accessible and/or adjoining rooms so there is grey area unfortunately.
That is how the ADA is having a field day with what the hotel industry is calling "drive by" lawsuits. I would just call and ask. If a property does not have the room type(s) you're looking for they HAVE to make a "reasonable accomodation" (which might include offering a suite at a standard rack rate) if availability allows. As someone in the industry, I hate to be a traitor of sorts, but when checking for availability for any sort of special room (whether is a balcony suite, accessible room, etc.) always open with a question of "availability" for your given dates. If the job is trained and performed correctly, the next question should be about room type. If not and availability is confirmed, they can be in big trouble. I imagine most places in LV would work to find you a suitable room or group of rooms though... =)