In all the race meetings I have worked as a marshall we are told that we are not to place ourselves in danger to get to or assist a rider.
But, I do know that the MotoGP marshalling is different as they have different 'corner crews' for different tasks. There are the flag marshalls, recovery marshalls, medical marshalls etc.
From my understanding the 'recovery marshalls' have the job of clearing the bike debris from the scene and if that means it can be restarted and the rider resume, than so be it. To me, if a rider can benefit from this work, then it is acceptable and not against any rules.
Edit: True Story.
I know of one 'recovery marshall' who has a collection of bike bits from various MotoGP/WSBK meets that they have worked and he has each labelled with teh dat/time/rider etc
Garry