They may use nest boxes where they are I have one Muscovy female who like the height of the chickens nest boxes and will use them occasionally. They like height too lol.
I have Muscovy and my chickens in the same house my female Muscovy roost on 2x4 right along with the chickens only my drake sleeps on the shavings mine don’t use a nest box they lay their eggs under the poop boards in the deep shavings I have up under my roosts gives privacy and out of the way...