Yes ItemObjectSpawner is used to spawn ItemObjects anywhere in the scene.
What do you meant by Item ID? You might be confusing the Item ID and the ItemObjectSpawner ID, they are two distinct things.
The ItemObjectSpawner has an ID such that you can find it anywhere in the code. All you need is to add an ItemObjectSpawner component somwhere in your scene (I would add it to your "Game" game object), make sure its ID is unique if you have multiple ones.
The you can get the ItemObjectSpawner with the id using the Get Global function, from there you can spawn an ItemObject:
Code:
var itemObjectSpawner = InventorySystemManager.GetGlobal<ItemObjectSpawner>(id);
itemObjectSpawner.Spawn(itemInfo, position);
I believe the Demo Scene has an ItemObjectSpawner on the "Game" gameobject so you can see how it's setup. The only requirement for the prefab is that it must have an ItemObject.