The green brittlestar is a known predator in the wild, and can and will eat shrimp, snails, small fish, etc at times. Not all will do this, but there is no way to know which ones will.
Other species of brittle/serpentstars may also do this. They all will, without a doubt, take advantage of sick, weak, dying or dead animals, whether snails, polyps, fish, etc.
The chocolate chip star is not reef safe. It will graze on many things...but FWIW, if you only have LR, than there isn't much trouble. They will eat little critters, but if you don't have a reef then there is not much issue in it. If you have a reef, and have a reef safe Linckia, it is still chowing down on critters on the LR, including sponges and tunicates, algal/bacterial films, etc.
Again, the definition of reef safe needs to be clarified in each situation. Generally, choc chip stars are kept in FO or FOWLR tanks.
General comments:
All seastars and brittlestars are intolerant of changes in salinity, pH, alk, etc...water parameters should be pristine, and not fluctuate. This is why the tank should be a good 6 months old before considering one, IMO.
The acclimation should be very long, 4+ hours, best using a drip method. Many, many of these guys die within a month of introduction, from acclimation shock.
IMO, brittlestars/serpentstars and non reef safe stars should be spot fed.
Brittlestars/serpentstars will not typically spend time in the open, so avoid them if you want something on display, or if you have any animal you can not part with, or, if you have triggers, puffers, or other aggressive fish.
The spines on brittlestars are defensive, primarily, and are no indication of particular diet that we yet know of (though some filter feeding species have very long delicate spines).