Last year I used a hen to do this and this year I wanted to do it again..... Are there any problems with this and will the other ducks bother with the chicks?
No problem with them they tend to be messier than chicks, and mama goes nuts when her babies try to "drown" themselves A.K.A. go for a swim.
If the hen sits on duck eggs your chickens will think they are another chicken just like having a mixed flock. Make sure there is some where for the duck to swim tho (that's very obvious lol)