When you Enable Editor Tracking on a dataset, the tool creates four new fields; "Creator", "Creation_Date", "Last_Editor" and "Last_Edit_Date".
You have the option of creating these fields ahead of time and passing your custom fields as parameters to the tool, but if you don't do that the tool will create the fields for you using the above default field names.
The problem however is that when you run this tool, if your custom fields do not already have values or you allow the tool to create the fields for you, all of the fields will contain <Null> as the value.
While the "Last_Editor" and "Last_Edited_Date" fields will eventually get populated with a value whenever someone edits that record, the "Creator" and "Created_Date" fields would never be populated with a value under this situation and you cannot calculate a value into Editor Tracking fields.
As a workaround, you can create the fields on your own, calculate values into them and then run the enable editor tracking tool on the dataset and pass in your custom fields - but that's an extra step that just adds unneccesary overhead to the workflow.
Please create an option in the Enable Editor Tracking tool to use the executing user's login id and current date and time to populate the "Creator", "Created_Date", "Last_Editor" and "Last_Edit_Date" fields in the dataset when running this tool.