eh, question.....
it would seem to me that if his medical has expired, he can't even fly dual with an instructor/examiner! So, I would think for that reason alone the instrutor/examiner should have to check if it's current! Even flying dual is performing the rights of the license, which requires a current medical.
And I would think you cannot sign off a license which doesn't COMPLETELY meet all requirements! He must get his medical, THEN go for the check/training ride!