Hermits will sit on and pick at anything. Usually just remove food stuff but they can be destructive. I've read that if you bury most of the tube in the sand the hermits can't get at the worm as fast as it can withdraw into its tube.
In any case, you may have to choose between the crabs or the duster. You may have seen here on TRT that many people opt out of having crabs in their CUC because of their crawling all over things and sometimes eating at / or on things.
yeah the hermits are driving me nuts because they are always sitting on top of the duster picking at him. I dont see any damage to the duster but i still think the hermits need to go. My tank is only a month old and the duster and hermits are all i have in it. im waiting another month or 2 till the tank is fully cycled before i add corals. i def dont want the hermits picking at those
Big hermits are bad at eating dusters and other worms. I had a large red hermit that never damaged anything in 2 years before it decided one day to destroy most of my X-mas tree worm rock. Destroyed all but 2 tubes before I could remove him.
I've never had issues but I also don't watch too closely. My lime green wrasse has snatched feather dusters regularly, which is why he's now in my fowlr (only has star polyps, some leathers, and a few shrooms)