Since this is an old thread, I hadn't seen it before. Actually, the idea that carrageenan is harmful to human or animal health is quite controversial. The study with arthritic rodents was done by surgically implanting carrageenan pellets into their bodies--the arthritis was not induced by ingesting carrageenan.
There are many health uses for carrageenen. See this article on webmd:
CARRAGEENAN: Uses, Side Effects, Interactions and Warnings - WebMD
Also read the wikipedia article:
Carrageenan - Wikipedia, the free encyclopedia
Undoubtedly, there are people and animals who are allergic to carrageenan. If you have a dog who is having digestive or joint problems, carrageenan is one item to consider eliminating to see if their health improves, but I wouldn't automatically avoid a food just because it contains carrageenan...