Megan, it certainly wouldn't have been a great goggle picture in those conditions but even in very low light levels they are far better than the human eye and, with a visibility of 1 km, they most certainly would have seen the rock and definitely seen the lighthouse beam.
Like many ex-mil people, I have used NVG in ridiculously low light levels - sometimes referred to as 'Red Illum' - and they still work and you would always want them instead of the naked eye.
I have also used them extensively over the sea and coast in similar and far worse weather to the accident crew and, only if you completely enter cloud, do you not need your goggles.
When worn correctly, you are able to look under the goggles to see your instruments, including MFDs with map, weather and radar information and then lookout through the goggles - best of both worlds and exactly how they should have been operating that night.
You can read all you like in a report but the only way to really appreciate NVG is to use them.