P.M.
Plenty of kids sleep through peeing, and a number I've heard about sleep right through pooping, too, or at least don't get aroused enough from sleep to deal with it in any other way. Night training often takes longer, sometimes years longer, than daytime potty learning. Kids really can't help this.
If your son is fighting you about using the potty, there is WAY too much stress and pressure for potty training to succeed for him – at least if you define potty training as his becoming willing and able to use the toilet when needed. He may technically be "able," but it sounds like he's anything but willing. Somewhere along the line, it became something his mommy wants him to do, but not something he wants to do himself. Toilet learning is a step toward autonomy and self control, so looked at that way, parents forcing the issue can actually stall that development.
And often when that happens, poop is withheld as long as possible. Occasionally, the body rids itself of the waste when relaxed in sleep. Inconvenient as this is, it's much healthier than two other results: constipation, or a much more difficult medical condition called encopresis (google this).
I've known quite a few moms who finally stopped fighting and let the child return to diapers, despairing and expecting the worst. Surprisingly, several of those children decided to be trained shortly thereafter. They just needed to have control of the process. A couple of the other kids took longer to get interested again, but still got there before the age of 4 or 4.5.
Very few kids can be successfully battled into using the potty. I'd try backing away from the process if I were in your position. I'd tell my child gently that he will get to decide when he makes this move, and that I trust him and am confident that when he's ready, he'll have an easy time of it. Your quiet confidence and respect could make all the difference for him, though he may hang back for a couple of months to be sure you are sincere.
Kids really do want to learn to use the potty when they are ready. It's as natural a part of their development as learning to walk and to talk.