For the person taking him up - has he ever tried to fly / land from the other seat? This in itself may take practice. Is he experienced in taking control with little warning, when the student gets too slow on landing?
Also the experienced pilot wont be used to pointing out mistakes in others, and wont be used to "teaching". They may also not be used to flying to a specific standard - rather they fly to what works for them. There is a reason that the FI course is so long...
There is a group at my club which is pretty much self contained. They have a well specced touring aircraft (archer) that each of them often flys alone or with friends but rarely with other pilots. None of the group members are instructors but they do their own checkouts. In observing the plane land very flat, almost on 3 wheels (tricycle undercarriage) at what appeared to be a high speed (for the umpteenth time) the club instructors approached various members of the group, suggesting a refresher might be useful, but none took up the offer.
Last weekend there was a prop strike after a bounce on landing.
Can they do it? Probably (yes unless insurance says no). Is it a good idea? You know the person better than the rest of us - but like everything in life, you will need to balance the risks.