snowflake eels are one of your best bets as far as housing an eel in a comunity tank. They mainly eat crusteceans as you can clearly see by the rounded shape of their teeth compared to the sharp daggers that eels such as a green moray have. They are likely to eat some smaller fish though if they are not fed regularly. Many semi aggressive fish will live fine in there such as hawkfish, shorp nosed puffers, and dwarf lions. And you could even get by with some more peaceful fish with caution such as clownfish. But to be honest, it really depends almost entirely on the snowflake eel. Some are extremely peaceful, while some others will eat just about any fish you put in there.
Damsels should be fine, the tank in the union at my college has a snowflake and assorted damsels and they have been fine for a long time, even with the snowflake being adjusted to getting live feeder fish.
foxface los comoe to mind, they are very neat, and they have poisonous spines so the eel probably wouldn't try to eat them. lionfish will work for the same reason, and would go great if you're makinga predator theme tank.