As far as we know this has not happened on itch.io, no. While your concern is understandable, I do think you may be over-thinking it a bit. Unfortunately, just as spambots are an inevitability on the internet in 2025, AI scrapers are, as well -- and if someone really wanted to use your project as material for AI scraping, whether or not it's tagged "no-AI" doesn't really have much of an effect. With the way that AI scrapers are utilized on the internet, many of them are not discriminating as to whether or not content has or doesn't have AI before scraping from it.
If you believe that a project on itch.io may be a result of AI scraping of your own content, please reach out to us and we will work to get your case handled.