Re: For those that use Ferber during naptime.
As long as he's "resting" I don't bother him. I have gone in and found him poopy though, so sometimes it's worth it to check in on him. That was before potty training. Now, it might be that he's holding it and can't go to sleep. I offer to take him potty if he doesn't go to sleep in 10-15 minutes.