as long as you keep the snowflake fed snails and hermits shouldn't be a problem, at least it hasn't been with mine, he's about 16 inches and hasn't eaten a single one of my hermit crabs yet
Saltman---
is you have time, do a google search for "reef safe eels", there are a number of nice articles which describe some decent husbandry on the eels you mention.
And YES.... the pebbletoothed eels (like snowflakes, zebras, chainlinks) crack crab shells like nothing. Thats what they eat in the wild , and thats what they eat in your tank.
BTW, I find my zebras to ignore snails
anything that will not fit in his/her mouth. IMO i would stay away from triggers, they tend to nip and cause stress. you can put more than one lionfish in a single tank as long as the tank is big enouph and there is enouph hideing space for the both of them. eels are great tank mates (again aslong as there is more than enouph rockwork IE hideing spaces for both the eel and lionfish)
Jake