Hi
Its not mandatory that RA agent service account will have administrator role of the machine, it can run with other permissions as long it will have proper permissions executing the required actions (e.g if its need to copy files to a directory - it must have write permission to that directory)
Note that for the agent installation you need admin rights as you will need to have permissions to install the service etc...
On Linux box you can follow this guide lines if you want to install the agent as non root user
Deploy Agents - CA Release Automation - 6.1 - CA Technologies Documentation
The user that running the RA service need to have full access to the agent installation directory
In addition if you want to run processes with other users permissions you should check the following guidelines
Windows:Deploy Agents - CA Release Automation - 6.1 - CA Technologies Documentation
Linux:Deploy Agents - CA Release Automation - 6.1 - CA Technologies Documentation
Hope this help
Jacky