From a GUI perspective, I'm not sure what permissions you need, but also be aware that the actual RMAN logs are stored on the clients, and can be accessed directly from there as well.
The directory structure where the logs can be found would be as follows:
Where <Job ID> is the actual job ID from the backup history. Under that directory you will find either a "backup.out" file or a "restore.out" file depending if a backup or restore was performed. This is the actual file that gets accessed by the GUI when looking at the job from backup history.
Note that "/opt/commvault" may differ based on what OEM platform was installed so think of those first two directories as the "install path".
Let us know if this helps simplify things.
Ernst F. Graeler
Senior Engineer III