The International Standards for the Professional Practice of Internal Auditing encourage auditors to acknowledge satisfactory performance to provide a balanced report. However, it is not a mandatory requirement. Including positive observations can help foster a constructive relationship with management and provide a more balanced view of the audited area.
Reference:
The Institute of Internal Auditors (IIA), International Standards for the Professional Practice of Internal Auditing (Standards)
"Internal Auditing: Assurance and Advisory Services" by Urton L. Anderson et al.