Can any of our followers answer this? Thanks. :)
Ok let’s see if I can get this right.
In the broadest sense possession can happen to anyone or anything. Trees become sylvan when they are possessed, corpses become animated corpses, golems become crazy death dealing tanks.
Mages are just ‘most at risk’ because of their connection to the fade and their frequent interaction with demons.
Abominations are ONLY those creatures or people who have been possessed that have magical ability.
Source: Dragon Age Wikia