Chicken sausage is completely OK for the diet; unlike beef and pork sausage, it doesn’t contain organs and other wierd parts of the animal. Also, I get organic chicken sausage which has only organic fresh ingredients; if you get the packaged stuff it’ll contain preservatives and perhaps even sugar! Hope this helps, I didn’t think it was allowed either but it is harmless. Boil for 15 minutes and pan fry it with some oil.
The fats in the sausage may be the only problem for you; this could cause constipation. I take a vitamin called A-F betafood to help digest these fatty meals (FYI).
Turkey and buffalo sausage is allowed also, but I haven’t gotten my hands on any yet.