if they use different article IDs they won’t be detected as duplicates, yes. feeds don’t actually matter, each article should have a globally unique identifier. it makes sense for same articles to have a same ID even if the feeds are different.
postgresql plugin would help but it would be better if the site in question generated the feeds properly in the first place.
also, you can make a very simple plugin which would work on those specific feeds and go by content or exact title match, i guess.