I'm pretty sure that I've heard of having a Niger in a reef but I wanted some input. I even think possibly Fshub had one at one time. Will he bother corals, hermits, snails or shrimp?
I have heard that the Niger is the safest trigger to keep in a reef....but personally I'd prefer not to keep one. Heck I've got a dang wrasse that I regret adding and if I could catch the damn thing it'd be gone tonight. Info suggests that the Niger may be more likely to be compatable with a reef system...but personally I'd not risk it...unless I had a very large system and was convinced that it would not snack on crabs/snails/shrimp.
The niger will probably not pick at your corals but you might want to watch out for the water paremeters. Triggers eat more heavily food like krill that makes them crap more which can bring the ammonia and the nitrates up.
i had a niger in a my 90 gal. he was an almost perfect citizen of my reef tank. he never bothered any fish, corals,shrimp or crabs. my cowfish used to steal food out of his mouth. he did seem to have a lot of fun plucking my snails off the glass and watching me have to turn them right side up. the only reason i sold him was because he and the picasso just produced way too much waste for a reef tank. they really are fine tuned crapping machines. unless you have a tank larger than 150 gallons i would not recommend keeping this fish. the growth rate on these fish is scary. when i bought him he was no bigger than 2.5" and after a year he was at least 6". their great fish, but you really need to have a big tank to keep them. heres a pic.