TLDR: OpenAlex generally covers everything in other databases, plus a lot more (depending on the database).
You don't have to take our word for it; there's a growing number of peer-reviewed studies showing this. We'd suggest starting with Culbert et al 2024 and Alperin et al 2024.
If you want to check to see if specific papers are in OpenAlex, you can search by title or DOI in the openalex.org search bar. For instance, try pasting doi:10.1111/j.1529-8817.2012.01224.x into the search bar and the paper should come up as a suggestion.
If you want to search OpenAlex for many papers, you can look them up at scale by running DOIs through our API. You can also use a third-party tool like the Open Research Converter to turn a long list of DOIs into OpenAlex work ids. If you don't have DOIs you'll need to resort to matching based on title and authors, which has been famously annoying in bibliometrics for decades.