Yes, most of Spine's types and objects are not Unity objects so they are not normally visible in any form as assets or inspector items.
You have to get references to them as C# objects.
For example:
var skeletonAnimation = GetComponent<SkeletonAnimation>();
var slot = skeletonAnimation.Skeleton.FindSlot("my slot"); // returns a Slot object.
There are many more examples of code like this in the Spine Examples sample scenes and code included with the runtime. Look for the "Spine Examples" folder.