Sorcerers are people just like you & me, with body, mind, soul & spirit, although we are following different masters. They practise the use of evil power for divination or manipulation of the natural world for specific ends, hence keeping in company with demons & evil spirits from the undead plane.
Some sorcerers may not understand why I'm always ready to ward off their pet demons at sight, even if not targeted at me. It's because my belief is such that demons & evil spirits should be back home to their own planes and stop doing wreckage in our life. Sorcerers are just being used as tools by their masters & their greed for powers to bring them on & increase the foothold of the evil in the land.
In short, the sorcerers are not undead, although there are times when they take a form other than human.
Some may have sold their souls to the evil. Some may have made a pact with the evil. The bondages there all seem unbreakable, because of the powers that are involved, but all it takes is just one Sword, the one & only one -- Truth.
Grace, who'd never make any pact with the evil for the Light, Apollo, Mercinae & the Bards