Does CA have the ability to isolate roles. For example, can a developer become the tester in the same user story/project. How is that controlled?
Agile Central (Rally) product does not have Segregation Of Duties as a concept within the product. Identity Management or Provisioning products mostly have that functionality. However, from Agile's perspective the easiest way to achieve this will be to create separate usernames for each permission you need for the same project: for example one user being a Project Admin, the other being a User etc.. - You can (if you want) have the email address of these users be same and point at same mailbox for the actual person.
I hope this helps. Let us know if further questions.