The instructor must be either an IAA Approved instructor or an EASA examiner.
Andrew - its the other way round: you need an hour (in total) training with a EASA Instructor to complete the SEPL re-validation requirement for a simple sign off involving paperwork only. Should you not complete (or not wish to) the full requirements then you have the option to undertake a licence proficiency check (LPC) with an examiner 'recognized' by the IAA. If the EASA Examiner was not issued with the authority by the IAA directly then they must have registered with the IAA and have been accepted by them.
If the EASA Instructor you fly with is issued by the IAA then the instructor may sign the paperwork as long as the flight with them completes all requirements. Otherwise, it needs an examiner as described above to sign the paperwork.