FFF,
The flying club employee is being asked to be a PASSENGER with a qualified pilot doing the flying. The employee is then being asked his opinion of that person's flying. Now, you, BEagle, SAS, the CAA, or anyone else, may not think this is a particularly good idea. But I can't see how it can be ILLEGAL.
Personally, if my flying is a bit rusty I like someone else there, since two heads are better than one. Not two sets of hands and feet - as SAS says, that's not a good idea - just two heads. Someone to remind me of things if all doesn't go according to plan and I get a bit over-loaded. In my albeit fairly limited experience, what usually happens under such conditions is that I'm a bit behind the aircraft, and tend to forget things like radio calls. Having another pilot to monitor things can make all the difference needed.