I have read people here who have but I would think you get better results setting them to incubate on their own. They each have different humidity requirements. The ducks are waterfowl and the hen is wet often. Turkeys are poultry, not wet at all. I have goose eggs going and they are in a bator all to themselves with a much higher humidity than my orpington eggs.
Maybe someone will chime in with more experience and we both can learn something from it.
Yes, you can definitely incubate turkey eggs with duck eggs, you shouldn't have a problem incubating and hatching them together. The humidity requirements aren't that different, the only thing I could see someone recommending is occasionally misting the duck eggs, as this will help them lose the correct amount of moisture so they hatch like they should. I find this works well when hatching ducklings and chicks together are well. I have had no problems with mixed hatches in the past, as long as the hatch dates are the same.
Turkey eggs tend to need a little more humidity than chicken eggs, as turkeys naturally nest on the ground and pull the extra humidity from the leaves and soil that they build their nests with. Ducks often give extra humidity via bathing daily and getting back on the nest with wet feathers. Humidity actually helps the eggs lose moisture content, which is why the air cell grows larger throughout incubation.
Just don't brood them together... turkey poults need their water to be real shallow and do better with marbles/shiny rocks in the water to attract their attention. Ducklings need their water to be deep enough that they can put their bill in past their nostrils so they can wash any excess feed out of their nostrils, to prevent sinus infections.
LOL, as of right now I have quail,turkeys,geese, duck and chicken eggs in my hatcher and all were incubated together.......the little quail look at the geese like what the @*#@#^ are you???....lmbo......