Does janusSEAL for Outlook create subject line protective markings that comply with the Email Protective Marking Standard for the Australian Government?

Yes. In the ABNF syntax used by the standard, janusSEAL products can create subject line forms according to:

  protective-mark-short-form        = classification              ; as defined in
                                                                  ; AGIMO Protective
                                                                  ; Marking standard  
  jS-2-protective-mark-medium-form  = protective-mark-short-form
  jS-2-protective-marked-subject    = "Subject:" unstructured
                                        "[" jS-2-protective-mark-medium-form
                                        "]" [FWS] CRLF