bapfreak
Welcome to the forum.
As you may have noticed this Forum is aimed primarily at Traditional things and plastic sabots being fairly new inventions don't fit too well.
That said, your questions still need to be answered.
A few of the posts gave some good answers and now I'll give you my opinion about using pistol bullets in sabots in your muzzleloader.
Most of the muzzleloading rifles have fairly deep rifling grooves and plastic sabots tend to either foul up these deep grooves with plastic or not seal the bores well or both.
The guns that are made for shooting sabots usually have fairly quick rifling twists like 1:28 and shallow rifling grooves.
As was noted, pistol bullets are designed for pistol velocities. While the solid FMJ (Full Metal Jacket) bullets will work, the hollow point bullets when shot at rifle velocities tend to blow up on contact giving very poor penetration. In other words they shouldn't be used for hunting in these guns.
Pistol bullets are usually fairly light weight so they offer no real advantage over roundballs.
Pistol bullets plus the plastic sabots cost more per shot than patched roundballs or solid lead bullets.
Solid pure lead bullets will work in most of the guns with 1:48 twists and they offer better penetration than pistol bullets. They also are larger in diameter than a saboted bullet so the wound they create is larger in size and does more damage.
Hope this answers your questions.