I agree that flying approaches to structures, rigs and vessels off-shore at night is considerably more harrowing- and it is definitely not a piece of cake in the S-76. But night flying in the USA in the GOM is generally limited to patient transport and cargo (at least with my company)- we rarely ever transport personnel off-shore at night.
The SAR factor has always bothered me as well, especially when going out deep.
I do not see a valid reason why personnel need to be moved at night. Seems ridiculous to me.