Unturned's character rig is terrible – so using existing animations is recommended for your sanity.
- Ensure scene unit system is metric with unit scale set to 1.0 and length set to meters.
- Select the Skeleton node.
- File > Export > FBX
- Selected Objects: True
- Apply Scale: FBX Units Scale
- Add Leaf Bones: False
- Primary Bone Axis: +X
- Secondary Bone Axis: -Y
Note that the Item.prefab from Unity is attached to the left or right hook with a local rotation of (0, 0, 90).