Alan size of the hawkfish and the shrimps is the main issue get the shrimps fairly large, I have kept a longnose for years before with cleaner shrimps with no obvious predation, however one thing you must do is add the shrimp at night when lights are off , this gives the shrimp time to find its cave and establish itself , if you pop it in during the day it looks to the fish like you popping in some skittish food! also fireshrimp are not as well recognised as cleaners as the common cleaner and are much more shy and less likely to be seen often.
It is possible to keep lionfish with fish that they cant swallow same applies here, if the hawk perceives it to be big for a meal it often wont try to eat it