Humus are def more peaceful then clowns. As far as snowflakes you may not see the entire eel all the time, but most of the time mine has his head out of the rock "checking things out" Come feeding time, he is all over, both him and my puffers will eat right from my hand.
If you do decide to add the clown trigger I would def add him last and watch him for a few days to see what happens. Like people I think fish tend to have different aggresion levels, and you may get a mean one, or a not so mean one. If there are problems be prepared to move your rock around, mix up the tank, so there are no territories preset.
Mit freundlichen Grüßen