Basically... splunk-system-user is the user all "system" jobs run as. For instance, if you check out the Activity Menu>Search Activity>Search Activity Overview, you'll see what the splunk-system-user is running... and it's likely summary refreshes, report accelerations etc...
"nobody" is what you'll see when something (dashboard, search, etc) has been given APP level permission. A specific user might be the "author"... but the user that "owns" it will be "nobody" since it's "owned" by the app...
With Splunk... the answer is always "YES!". It just might require more regex than you're prepared for!
