All of my ducks except 2 Cayuga and 3 buff egg layers are Muscovy. If Muscovy don't get protein as in bugs, snakes, rodents and yes, raw meat such as deer they will get anemic and die. Good thing I live in Iowa and know about every deer hunter around. Deer season starts about the time the bugs die out. Weekly I get normally a full carcass with the loins and hind end missing. The front end and some meat left on spine etc is enough for the ducks until the next week, or next deer delivery. With out this, I would not have the healthy ducks I do. The bones are then dried and my neighbor burns them in their stove at night. They burn hot and slow so they don't have to get up in the middle of the night, and they don't smell if they are dry. I remove them in the spring by the wheel barrow full. The ducks eat rather well.
As for duck meat, I have never done it, but I know people that save the duck fat to cook potatoes in, or spread on toast like butter. Geese are greasy.. duck fat is known in some of the finest kitchens as a delicacy. I personally don't like fatty meats. I skin my chickens so I don't have it. I do freeze the fat (or skin) for cooking or when a neighbor would like some.
So.. in short, not more fatty then a farm raised chicken. Actually I think my chickens are more fatty. Remember though I have Muscovy and they have a different fat level then common ducks.
I have never eatten a duck that wasn't' a Muscovy drake, however I do plan to try it next fall as I will have some of my Cayuga that I won't keep, as they will be related. I have also heard they aren't like normal ducks either.. so? I don't really know, I may have to buy one and find out?