But we are talking about a government regulatory test of one pilot's instrument flying ability. It is not a crew operating on line and it is not training - it is like any examination - it is a test. Is prompting allowed in an examination? Of course not. While the support pilot should operate ancilliary controls at the request of the pilot under test then all decisions should be made by the applicant for the renewal or issue of the instrument rating.
See the earlier point, in the UK (and europe) a multi-pilot IR is ONLY valid on that type operating as part of a crew. So it's not 1 pilot that is being tested.
My point being if the PM is saying " 4 miles 100 ft low" that's fine it's normal ops. If the PM is saying, " 4 miles, 100 ft low, select 400 feet per minute and by the way you might want to go back to 600 in a mile and blah blah blah then that's not fine. There is a difference between normal deviation calls and just pattering the other person round. Again I'm pretty sure every CAA approved examiner I've met is well up to speed on it and is very good at managing the test. Can't speak for other countries.