Thanks again for all your help!
Finally, I could manage it to allow a certain user only access to Logs and Reports for a specific Security Gateway / cluster via Smartview with identities shown as follows:
Create a Permission Profile with only access to Logs and Reports (all options ticked for "Monitoring and Logging" & "Events and Reports") (see pic below).
Create a user with Permission Profile created before.
And then limit user's access to specific Security Gateway by modifying users.xml as described by @Dror_Aharony
At the beginning of my tests I had a strange issue, I created a new user and played around with the assigned customized Permission Profile. For whatever reason, I couldn't manage it for that user to get the identities shown in the Logs and Reports. Even when I assigned this user the "Read Write All" or "Super User" Permissions Profile, this test user had the identities only hidden (******) in the Logs and Reports.
Maybe I did something wrong with the order or creating/adjusting the Permission Profile or limit user access via users.xml. But anyway it should have worked when assigning e.g. the "Super User" Permission Profile. So it seems to be some kind of bug.
Maybe that will help someone who faces the same issue.
Best Regards
Nenad