If I had a Pegasus RIW account, can I use it to login to the RSW system?

Yes, you can! If you had an account in the former Pegasus RIW system, you will be able to use those details to login and find your workers in the RSW system if you are working for a Pegasus RSW Partner. All the information you had in the Pegasus RIW system will be there when you login.