The Default worker is the main Windows process of EasyMorph Server. By default, it runs under the NT AUTHORITY\LOCAL SERVICE account after installation. However, it's not obligatory. You can change it to a different account in the Services panel of Windows as described here: How to change service account.
It means you can run even the Team edition under an account different than NT AUTHORITY\LOCAL SERVICE. However, if you need your Server spaces to operate under at least two different accounts, then the Enterprise edition is required.