Yes the JSS will show you the username of the management account that's been made for a particular computer. In the computer's properties in your inventory view you will see "Managed: Managed By..." followed by the username you created as the management account.
If you ever create a new QuickAdd package, the management account you create in that QuickAdd package will be put on any computers that you run that particular QuickAdd package on. There's no connection between multiple QuickAdds, what matters is the package you run on the computer.
You don't need to rerun QuickAdd packages to change the management account, you can change it via a task called Management Account on the JSS.
How you use management accounts is up to you, you may want to give your help desk or admins a login account which isn't the same management account Casper uses to install things, then you can differentiate between what's being done on a system, whether it was Casper doing something or a IT staff person that logged in. If you wanted to do that, the account Casper uses to install programs and etc can have a completely randomized password that's unique to each computer because a human does not need to use that account.
If you ran a computer lab in a school and there was an admin account that was being used by teachers and student workers to do maintenance or service, you wouldn't want that to be the same admin account on staff or administration computers since it has the same password, a password that could be easily leaked.
