It’s not exactly what you’re looking for, but this great script by @TfTHacker is excellent for grabbing Hypothes.is annotations into Obsidian. I’ve been using it with Raindrop for a little while now with some success. Pretty simple workflow: collect in Raindrop → annotate in Hypothes.is → bring the annotations into Obsidian.
Sorry, don’t know of any way for Obsidian to search externally - I just pull my external notes in so I can search it all from within Obsidian.
Perhaps someone else has an idea about that?