Thank you for your post.
Return to the Relationships graph in "Manage -> Database". Between the two tables is a line that has an icon in the middle. Double-click the icon, and information about the relationship is displayed. Since you want the ability to add records from either Data Entry or Employees table, check the option on both sides for "Allow creation of records in this table via this relationship".
Now, when you enter an Employee ID, and the other file doesn't have the data, you can add the information to the other file. I assume you want this to happen automatically, so you'll have to create a script that either copies the information from one table to the other or switches to the other table and does an import. The choice is yours.
If you need clarification for any of the above steps, please let me know.