The following summary of Worldwide Helicopter Offshore Accident Causes observed that in around 1.2 million hours of operation by some 1,440 helicopters between 1997 and 1998, there was not one Engine related accident in Multi-Engine Helicopters and as I don’t know of any 3-engined Offshore Oil and Gas helicopters, statistics would suggest that Multi-Engined operations with just the two donks is clearly not proving to be a safety issue.
http://www.ogp.org.uk/pubs/300.pdf