(1) It can support it.
Here's where animation updates happen in standard Spine-Unity's SkeletonAnimation component: https://github.com/EsotericSoftware/spi ... ion.cs#L97
For your purposes, you could have a new class inherit from SkeletonAnimation and only have this in its body:
public override void Update () { }
void FixedUpdate () {
Update(Time.fixedDeltaTime);
}
The other option is just to modify SkeletonAnimation itself, remove its Update method and add this FixedUpdate method.
That'll make it work.
(2)
Select the SkeletonDataAsset (the file with the spine icon) in your assets/Project panel. Its inspector has a preview window.