That’s the thing, they aren’t scraping IMDb, they scrape other sources that have the IMDb ratings from what I remember. Directly scraping IMDb is not a good idea if you make money off it.
I don't think the distinction matters if imdb wanted you to stop offering their ratings in your commercial api.
I certainly expect that this project is too small of a fish for imdb to care either way. It's more of a curiosity for me since I always love the simplicity of an API as a business.
You can do anything until you get caught. However, I think there are many companies that exist in the realm of "data aggregation", likely walk a fine line though.