Never done it, but I would not unless you had a skinny duck. The fat layer on a good bird would mess up the deep-frying action.
I'd find a skinny duck (gadwall, maybe?), then brine it for 12-24 hours in 1/4 cup salt to 4 cups water, then dry it very, very well inside and out -- then give it a go.
I'd think 325-350 degree fat until the skin is golden brown would be good...
I love all of God's creatures, properly prepared.