In a Triggered Smart Campaign, is there a way to identify leads that were just imported in any List across my Marketo Workspace?
'Added to List = is any' is not good enough sine it will also identify people who were added by Marketo flow steps which are not List Import.
You should always import in dedicated, separated lists that can be used to easily identify the leads that where imported. Furthermore, it will also give you some interesting constraints in the "person is created" trigger and "person was created" filter.
Here's an example for a live event: Let's say we have a list of attendees that we need to import. Create a static list called "attendees" within your event program. Then in the smart campaign directly reference this list. Simple. Done.