The 'D' value of the 609 is about the same as a Bell 212 (60ft vs. 58ft) which has been operating to rigs and platforms around the world for decades. The advantage of the 609 is that the pilots can see the outer most rotating bodies of the aircraft (the proprotors) while maneuvering on the helideck, whereas we cannot see the same in our 212s (the tailrotor).
Add to that the fact that 609s no longer have the potentially fatal problem of having pax walk into the tailrotor which is an exponential leap in safety for deck handling ops.