Zebra moray bite fells like a getting your finger caught in a pair of pliers but not as bad. I wouldn't worry about them biting you as their mouths are smaller than most morays and unlike other morays, which will pull back and not let go when biting, resulting in rips in the flesh, Zebra will let go, it's also very easy to pull you finger out of their mouths if they do bite you. Either way you shouldn't be putting your finger or hand near any morays and specially the mouth. If you do get bitten make sure you wash your hand off really good as morays carry bacteria in their mouths.
In the wild Zebra morays use their teeth to crush all kinds of shell fish, and will do the same in your tank, so any hermit crabs maybe at risk of being eaten. There isn't a need to worry that Zebra morays need shell fish to wear down their teeth as people have been keeping Zebra morays for years without feeding them live/died shell fish, with their shells, and never have had any problems with the teeth growing to large.