If the non-instructor but experienced person on type is acting as 'safety pilot' and is there to only share knowlege or take command if required that will satisfy the requirement in my view. I'm not convinced that the safety pilot can act as crew and log anything. If I'm right then the pilot new to type logs PIC. The safety pilot will only log PIC only if they are required to take over.
Remember, the pilot being checked holds the requried licence and rating(s). However, for a reason other than licensing they are not entitled to be PIC.
The best example being that the insurance requires that all pilots are checked out. Until that requirement is complied with then they can not fly as PIC. Therefore the person you call "safety pilot" must be PIC - an insurance requirement.
Having established who has to be PIC, the only question is what the person manipulating the controls will log.
The situation is a clear example of a situation where the regulations (Insurance in this case) governing the flight require two pilots. Therefore, one will be the PIC and the other will be a co-pilot.
To say that either one was "a passenger" is to say that they took no active part in the safety of the flight operation. Or are you saying that passengers are also crew members???????
The only way round this situation would be for the rule to be changed from one requiring a checkout to one which requires new pilots to "only fly when accompanied by a single passenger who is a designated current pilot and member".
That makes things clear - one is PIC and the other is a passenger.
Remember to check you'r insurance requirements and policy very carefully. Often passengers receive more compensation than crew in the event of an accident. Therefore insurance companies who recognise the increased risk in checkouts can ensure that at least two seats are occupied by "crew" and thus limit their liability during the "checkout".
If you are the person who does the checkout - check your liability insurance also. It may be covered by the club / group insurance but if not then the last thing you want is to be in court countering a lawyer who is highlighting the fact that the (now deceased / seriously incapacitated) pilot was clearly not competent and should not have been released, and you had no qualifications or proven training in assesing pilots.