Yes, they can live together, they are not as bad as cockerels - but you'll have to watch your duck / drake ratio during the breeding season. Sometimes they can hassle the ducks too much - one goes to mate and the other will rush over and the ducks will suffer. At this time of year once the breeding season draws to a close, and over the winter, they should be fine.
Perhaps plan for either getting rid of, or separating during the breeding season or maybe add more ducks so the ratio is better.
I have 3 drakes running with 2 ducks at the moment and since there's no breeding, they are all best of friends.
Tim
