Welcome to Community! Adding an employee who is also a sub-contractor in QuickBooks Online can be accomplished in a timely fashion. I would be glad to help!
When adding an employee who is already in your books, you'll see a pop-up message indicating this contact already exists. To bypass this error, you'll simply add an identifier to the last name of your sub-contractor, such as an (*), to prevent any error messages. Once you've made this change to the sub-contractor, you're ready to set up your employee, by following the steps in this helpful guide.
If you have any other questions, please reach back out. We would be happy to assist!