There are other issues. Pea-brain said that "disease and parasites are very uncommon with stomatopods". From what I understand, this is not necessarily the case -- just that they are not well-described (or understood). There are the well-known "shell disease" issues as well as species-specific disease issues (like fungal disease in H. californeus (sp?)). It is uncertain how many "random deaths" are due toxins or some (unknown/undescribed/unresearched) disease process.
A little "closer to home", many areas require special permits for collection. I know that is the case in San Diego. Also, local shellfish are dangerous to eat during certain times of the year due to the presence of dinoflagellate ("red tide") toxins. We have an active red tide now, for instance, and filter feeders would likely have toxin accumulation. I certainly wouldn't feed a local snail to my peacock. Those toxins are NASTY.
Long story short, I wouldn't risk it (either from a legal or safety perspective).