Why don't you just put it in the query:
Query for employees with invalid managers:
Select [Employee_Name],[Employee_Status],[Employee_Manager]
FROM employees
WHERE [Employee_Status] = 'Active' AND isNull([Employee_Manager])
Query for employees with valid managers:
Select [Employee_Name],[Employee_Status],[Employee_Manager]
FROM employees
WHERE NOT ([Employee_Status] = 'Active' AND isNull([Employee_Manager]))
Query with the column displaying if the manager is valid or invalid
Select [Employee_Name],[Employee_Status],[Employee_Manager],
Iif([Employee_Status] = 'Active' AND isNull([Employee_Manager]), 'Invalid', 'Valid') as [Manager for employee]
FROM employees