Yes, I suppose, even though there are not many articles dealing with this subject.

These plants are generally described as having high crude protein contents (per kg of dry matter), and such protein is almost completely fermented in the rumen.

Here is what I could find, this might give you a few ideas:

http://www.lrrd.cipav.org.co/lrrd7/1/3.htm

http://www.lely.com/en/farming-tips/duckweed-as-cattle-fodder

Yes duckweed can be utilized as fodder but its quantity might be small. These can enhance productivity of animals as they had high CP content. Regards 

Composition varies greatly depending on the growing conditions. Here is a link that addresses some of these issues. It could be used for livestock, but it needs to be dried to provide adequate nutrients, because it is too wet when fed "as is".

http://www.fao.org/ag/aga/agap/frg/LRRD/LRRD7/1/3.HTM

Yes, duckweed can be grown and fed to dairy animals, small ruminants, poultry and ducks. One small pond of 4'X8'X1" duckweed would yield about 1/2 kg of green fodder protein on a daily basis at literally ZERO cost. Cows and buffaloes relish eating them, once they get used to them. Obviously, when dairy animals that are in -ve energy balance are fed duckweed improved milk yield and quality. Some State Animal Husbandry departments in India like Andhra Pradesh actively promote the growing of duckweed by small and landless farmers for feeding it to their animals.