So do we know what causes the Bosmer to transform and begin the Wild Hunt? Obviously not willingly, since they seem to be ashamed of it. And does that passage in the Pocket Guide to the Empire really suggest that all wild life, or at least the more monstrous ones (mintotaurs come to mind) are Bosmer that began the Wild Hunt and never returned?
And is there any connection between Dagon's hunt and the Wild Hunt? Or is it just the same name?
Basically, a bunch of Bosmer get together and perform a ritual, allowing themselves to become monsters in order to achieve some goal, like killing King Borgas. Even though they do it willingly, I believe they view it as a last resort, due to its horrific nature. There's a great description of it in the book http://www.imperial-library.info/obbooks/dance_fire.shtml, in which the narrator is a witness to one. And yeah, [at least] according to the PGE writer's Bosmer companion, every monster in the world is from a previous Wild Hunt.
Dagon's Wild Hunt and the Bosmer Wild Hunt just happen to have the same name.