Mike,
No, you don't need to use a sabot when shooting lubed projectiles out of a modern inline muzzle loader. However, you're giving up most of the advantage of having the modern inline. You're limiting youself on muzzle velocity, accuracy, and bullet performance. Modern inlines shoot saboted bullets with a remarkable degree of accuracy out to some very long distances. You can shoot a large variety of jacketed bullets that are designed to perform very well at muzzle loading velocities. I've tried shooting lubed lead bullets out of my inlines to see how they perform and they shoot pretty good but they don't shoot as well as the saboted bullets and they don't perform as well on game. Don't get me wrong, I've shot a lot of deer with lubed lead bullets but I've also shot a lot with saboted jacketed bullets and I've shot them a lot further with the sabots. You might want to think about trying some sabots. Hornady and TC both package sabots and bullets togather and they work pretty well. Get some and give them a try. Good luck with what ever you use.