We just added idols a little while back to two of our tanks,
They will nip at feather dusters and obviously sponges, and I've seen on take a swipe a time or two at one sps colony when they were first added.
Now that they've experienced Nori, I haven't seen them touch anything else, even the sponges, lol.
We have a picture almost identical to your above pics, two idols behind our achilles, love the Hawaiian fish!