Rest and Sleep Talk take up two valuable moveslots that would have gone to coverage moves, so they're a waste. Pokemon like Swellow, Ursaring, and Zangoose rely on coverage moves to be at their maximum effectiveness; that, and they're not very bulky to abuse RestTalk. If you want them to keep healthy on a consistent basis, you'll need to run a Wish user on the team.
To answer your question, if that Pokemon wakes up, it will get poisoned by the Toxic Orb again at the end of the turn.