Yes, Cuban Whistling Ducks (Dendrocygna arborea) aka West Indian Whistling Duck, Black-billed Whistling Duck, etc. are listed as a U.S. migratory bird and as such need a permit to be sold/traded. Here's the link to the complete list: http://www.fws.gov/migratorybirds/regulationspolicies/mbta/taxolst.html
They are a large whistling duck and can be quite aggressive with other birds if not given enough space to defend territories. I've seen plenty in mixed collections but adult breeding pairs can be tough on other ducks and an isolation enclosure should be available should a problem arise.
Might I suggest (again) that you purchase the book Waterfowl: Care, Breeding and Conservation by Simon Tarsnane? I think it would be really helpful for young and aspiring waterfowl enthusiasts such as yourself to read this book cover to cover, maybe more than once. It's not the be all and end all of waterfowl books but it'll answer a lot of questions you post here. Heck, I'll even buy the darn book for you and mail it.