Ya. Been there, done it, bought the T-Shirt. OK so you are too chicken to change that Key field. It will probably work OK, but there is a Plan B.
Make a Sync table of the employee table and bring across the userid and the the Record ID# of the Employees table. Note that the user id will come across in text format and will appear as the email address or the user's "User Name" if they entered one. Most users never find that menu. Set the userid in text format field as the Key field.
Then on the Orders table make a field called
[Userid of Current User in text format]
with a formula of
ToText(User())
Use that in a relationship back to the Employee Sync table and look up the [Record ID#] of the Current Employee.
Then have a form rule
When Related Employee is blank
change [Related Employee] to the value in the field [Record ID# lookup form Syn table]
Set the checkbox at the very bottom to fire all the time (ie un check it)
