I'm sure you can trim nails should the need arise, but if a duck is kept on ground or natural surface, there shouldn't be a reason to do so. If kept on wire, it's more of a possibility. If you do decide to do so, look for the quick (blood vessel in the nail) and do not cut into it or it will bleed. On the off chance that you would trim and bleed, you should have clotting powder on hand to stop the bleeding.
Never had Muscovies, so I can't comment on that particular species.