Okay, to satisfy my own curiosity, I googled. I found lots of answers, both yes and no. Naturally, I gave more credence to the more clinical sources.
Here is one link:
And in case you don't feel like slogging through the entire article, here's the pertinent info:
Treatment. Various sulphonamide drugs and coccidiostats have been used in the treatment of renal and intestinal coccidiosis of geese. If the geese are to be fed rations which were formulated for other types of poultry, it should be noted that in spite of popular belief to the contrary, waterfowl can be fed rations containing most of the coccidiostats used for chickens. The Veterinary University of Hanover, Germany have specifically reported that the following coccidiostats found in chicken rations are tolerated by waterfowl: amprolium, amprolium-ethopabate, clopidol, clopidol-methylbenzoquate, DOT (zoalene), lasalocid monensin-sodium, narasin, nicarbazin, robenidin, salinomycin and sulfaquinoxaline. They also reported that neither halofuginone nor arprinocid are tolerated by waterfowl and that they could find no information on the effect of giving waterfowl feed containing either decoquinate or maduramicin ammonium.
And another link:
I found these and many more. And then I also found links that say the exact opposite. So, how does a person decide?
Personally, I brood all of my chicks outside, with broody hens, and I've never had a problem with cocci. I only use medicated feed when the feedstore is out of the unmedicated.
But I have a clutch of duck eggs that is due to hatch next week (My first ducklings ever), so the issue has special significance to me. Clearly I don't want to damage my duckie-babies in any way.
Not sure what to believe!