I used to have a Longnose and the only thing at risk really would be stuff like nudibranchs and shrimp. Hermits, snails, urchins, crabs, etc. should all be fine. I'm guessing there's some chance a crab caught during a molt might be at risk, but I never had a problem. Their mouth is really rather small and less powerful than something like a trigger or a puffer that can easily destroy every member of a CC.
It's also worth mentioning that small fish might be at risk. In my personal experience I kept one with a few clown gobies and a neon goby and never had any problems other than the longnose chasing them away from his perch.
Also I want to add that in reference to the book, longnose hawkfish aren't really comparable to most of the other hawkfish in terms of aggression and risk to tankmates and your CC. Unless specified, when books or people refer to the behaviour of hawkfish, they tend to be referring to the type of things you could expect from something like a flame hawk, arc eye, etc.
