Yes you can get good expansion with saboted bullets.
I am holding in my hand a Hornady 250 xtp, as you may know this is a hollow point. I shot a deer in the chest with this slug at 70 yards. The bullet went through part of the neck, through the right lung, and stopped just under the skin after passing all the way through the lung.
This bullet started at 250 grains, now weighs 182 grains. It is a perfect mushroom, max diameter 1 1/4 inches. It knocked the deer for a backflip, and it was dead right there.
Now, I am shooting a Savage and I am driving this slug at 2,300 fps. Other inlines that don't use smokeless will have a lower mv, and would not get as much mushrooming, but still would get good expansion with this slug.
You have asked a good question. Lots of guys have problems with saboted slugs not expanding, it depends what you shoot, and what speed. I have heard of the Hornady 300 SST not giving good expansion.
If you shoot the 250 XTP from the Savage, I guarantee you good accuracy, good expansion, and good retention of bullet weight.
I zero the 250 XTP dead on at 150 yards. This makes it 2 inches high at 100 yards. At 200 yards, it is about 5 inches low. I get 1 1/4 inch groups with this slug.
I can shoot the 250 SST and get better ballistics, 2 inches high at 100 and I would be 3 inches low at 200. The 250 SST is a proven deer killer, and will give expansion, but I prefer the XTP because it is a little more accurate, and gets a better mushroom, and it is cheap because you can buy it in bulk from Cabelas as a pistol slug.
I also know guys who have taken the high shoulder shot with this load, and gone right through the shoulder and cut the spine, no problem.
I would take a 200 yard shot with my rig, no problem. But, I would have to know the range, since I am 5 inches low at that range, if I know the deer is past 170 I have to elevate the aim point a few inches. I also would need no wind and a good rest. Two hundred yard shots with inlines are common.