Are sitters allowed to keep dogs on leashes 24/7 while they are staying with them in their home?

Rover sitters are independent contractors. They can do whatever they like and it's up to you to decide if you like them or not. I would not use a sitter who keeps them on a leash indoors all day.

I would say that is an odd practice to have a blanket policy for all dogs. Maybe she means for the first few hours so they can't get up to mischief and learn the rules of the house? Trainers recommended keeping dogs on a leash when they are pups and learning or if you are trying to break bad habits, so it wouldn't strike me as an unusual request from an owner.