"Reef Safe" is a term I hate. There is no real clear definition that is agreed upon by everyone. Is a lunare wrasse reef safe? They don't eat corals, but no knowledgeable reefkeeper I know would put one in a small reef tank for lots of good reasons. Instead, I find it easier to say what the fish will probably eat in your aquarium, what it probably won't eat, and what it might be a threat to. Your mileage may vary.
Odonus niger is largely zooplanktivorous in the wild. This doesn't exactly translate to the aquarium though. They will not eat corals, soft, stony, or otherwise. I have never heard of them attacking clams. They will definitely attack small or newly added shrimp, and any bite sized fish (royal grammas, chromis, small anthias) might be considered a meal. Small snails that they can dislodge from the glass are almost certain to get taken off eventually. Unlike some of the other triggers, they are very unlikely to attack starfish or sea urchins in my experience. Sponges are also on their diet.
When they get large they are very boisterous fish that need a lot of swimming room, and they do get very big (20" in the wild, around 12" in captivity). They tend to dig under rockwork to excavate a cave to hide in, which can bury corals and topple rockwork. They like to bite hands. They like to show dominance over other large fish. All in all, an unsuitable fish for all but very large (500 gallon+) reef tanks, in my humble opinion.
There are better triggers for reef tanks. All the Xanthicthys spp. (blue throat, sargassum, crosshatch) are peaceful fish that might only bother very small shrimp, if that. The blue throat is my favorite because it's easy to find, very beautiful, and doesn't get as large as the Niger. In the wild it tops out at 12". It still needs a big tank with lots of swimming room as an adult however.
Hope this helps,
Matt