Yes, pets are allowed in Sunriver. I'm shocked you haven't seen any! There is a leash law which is enforced by the Sunriver police. Most homes are second homes or vacation homes in Sunriver; whether a pet is allowed in the homes/condos is at the owners discretion. I don't believe Meadow House has any additional pet restrictions.
Typically property management companies will charge a surcharge to have a pet in a rental. Often there is a limit to how many pets and what sized pets (i.e. - dogs under 40 pounds) are permitted. If you look on any property management web page you should be able to search homes by Pet Friendly.
I am a Sunriver agent, have owned many rentals in Sunriver as well as lived there for 5 years. If you have any additional questions I should be able to quickly answer them for you. If you would like an active list of Meadow House condos (or anything else) for sale in Sunriver please let me know. My email address is firstname.lastname@example.org