If an employee is also interacting with your business as a customer (buying something from the business) or supplier (providing goods or services to the business outside their employment terms & conditions) then it would be reasonable to add them as a customer or supplier for that transaction.
Combined reporting of all of an entities interactions (Customer, Supplier, employee, Expense Claim Payers) with a Manager business has been discussed however is not yet available. I suspect that would require having a contacts database within which various roles could be individually selected Copy Customer to Supplier and vice versa - #2 by Patch