Peter I had a 2.5 inch (still have him) Coral Beauty with my Goldentail for 3 years. My Goldentail was 10 inch when I got him. They are primarily crustacean eaters, not fish, but that's not to say a hungry Miliaris wouldn't go after a 1.5 inch Occelaris (for example). I would think anything over 2 inches would be safe with the 14 inch Goldentail on DD, or the smaller "Banana" there. Mine was probably 14 inches when he died. I had real issue getting food to mine even with tongs, he was not an aggressive feeder and my big Lime Green Wrasse and Triggers made it hell getting food to him. I think he eventually perished due to that. I had a snowflake for many years that was a much bolder feeder, that ell is nearly 30 inches long and still alive in S. Carolina.
Back to the subject....anything over a couple inches SHOULD BE safe, and as long as you don't have 5 "food stealers", I think it's a great Eel, and you know getting from DD that it's eating well for sure.