I understand that Search Integration 4 Tridion (SI4T) can index binaries only if they are linked from other published Components (or perhaps Pages).
Can SI4T index, or be made to index, binaries coming from another system via the External Content Library?
Background
I'm reviewing a scenario where the same PDFs are uploaded and used separately in both Tridion Docs and Tridion Sites.
Sites indexes the PDFs using Search Integration 4 Tridion (SI4T).
To reduce the writer and editor steps, I'd like to recommend having PDFs exposed to Tridion Sites with an External Content Library (ECL) integration. PDFs can be uploaded and published once in Docs and reused in Sites as needed.