Yes - I think so... I recall any examiner can sign SEP revalidation by experience subject to the licence holder meeting all of the requirements for said revalidation.
It’s actually any UK Part-FCL examiner can sign for SEP/TMG Class Rating Revalidation by Experience in a UK licence.
GR is a national (non-Part-FCL) privilege, so the answer is -NO- when referring to Part-FCL licences. It specifically states this on the GR examiner authorisation.