Can you do it : yep.
Will it work well? not bad
chickens need 21 days, ducks 28, muscovie ducks 35 days
if you time it so that they all hatch together, that's better so you raise the humidity on hatch day
hmm: Scenario 1: chickens started, on chicken day 14 duck eggs introduced. day 17 stop turning the chicken eggs, or remove eggs and some racks from turner, raise the humidy for chicken hatch
the ducks eggs should not be damaged by raising the humidity during the hatch for two or three days. mother ducks take a swim daily so the eggs get a soaking (which actually makes the eggs softer and easier to hatch)
just watch that chicks don't get stuck in the auto turner
then raise humidity for duck hatch when the time comes. It should work out fine.
scenario 2: chickens day 7 duck eggs introduced: on chicken day 18 remove all eggs from auto turner, raise the humidity for chicken hatch and later for duck hatch
eggs really only need to be turned for 7 days
ideal would be a second unit for hatching
If the ducks hatch before the chickens, the ducklings will make a mess of everything, likely ruining the chicken hatch
I vote: Do it.