I think you aren't seeing an event in Osiris for that item event because it's not global. And since are creating it via template there is no way it will be global. I think you have the right idea about the Item Handle (and Template) being the only way to manipulate a non global item.
Yes, I'm also afraid that's indeed what's happening.
If ItemHandleToTransform doesn't work for you, maybe you can describe what you are trying to accomplish and there's something else you could do?
Technically, I could just make a bunch of global items, since their number and initial position is fixed. It's just nicer to define their properties completely as facts in a script's init section. It works fine for characters, since there I can do everything via the CharScripts.
What I'm trying to do is create platforms that move across lava, on which the player can walk/jump (I still have to figure out a way to make the character move along with the object, because by default the object just slides from under you once you're on it, but I have some ideas for that which I still have to try). And I hope no one at Larian will revoke my game license for the sacrilege of trying to implement some kind of jumping action inside the Divinity Engine
