I do not know what the physics shape of a sculpt is; however, I can say with certainty it is not the same as a convex hull torrus and you can prove it for yourself. Rez a sculpt or create a regular prim and set it to sculpt shape instead of box. Make sure the physics shape is set to prim if you rezzed one out of inventory.
Set the size large, say 64x64x64 so the changes will be more dramatic (and obvious). Copy the location and size of the sculpt using the C (of the CPp) buttons. Rez a torrus and paste the location and size using the P buttons. Get on top of the torrus, walking to the center of the divot. Change the physics shape to Convex Hull. When you do, you'll rise. Set the sculpty to phantom and you'll fall. Ergo they do not have the same physics shape.
Now maybe you're thinking I forgot about rotation, but I did not. You can check for yourself if the rotation of both is set the same you will always fall when you make the torrus phantom.