Ima local and know for sure that the Rio allows dogs.... Its kind of funny going through the casino and seeing dogs walking through with their people.... Ive seen big and small dogs there, so ya may want to check with the Rio direct....
On another note... I have a house in summerlin (bout 15 miles from the strip) and was thinking about renting my detached casita out during the WSOP.. its adorable, quiet and in a great neighborhood. It is a studio with walkin closet, full bath, fridge, locked gate entry, cute court yard and near the 215... just sayin