IM O:
If you are a required member of the crew - ie. your company training manual (part D under JAR OPS) requires the presence of a safety pilot for the certain training duties, then you ought to log the hours (as I was told by my TCs, many years ago).
The hours still count towards your maximum annual flying hour total (UK? 900hrs), so they should go in your logbook for that reason alone - one of the reasons we keep logbooks in the first place.
I agree with BOAC regarding 'accountability' - though I consider that quite a horrible concept in aviation: as professionals we should be trying our damndest to get it right all the time, regardless of who is 'in charge' or paper.
If one is on board, and a situation develops, one had better feel able to do all possible to assist, to the very limit of one's capability - if not, one ought to quietly choose another career..!