I have one in a tank by herself with a bunch of live rock and a couple of coral frags. She is entertaining enough by herself whether she's just hanging out between some rocks, walking on her fins, bobbing her lure, or eating. My girlfriend says she's more like a dog.
I have considered trying her with a Zebra Eel for 2 reasons. A) Zebra's tend to be peaceful toward fish, and B) Unless the Angler's a Commerson or other very large Angler, it most likely won't try to eat something as long/large as a Zebra Eel.
As for now, I'm content with just her in the tank, and I don't want to compromise her by adding a possible disaster scenario.