They mainly use TransUnion. Yes they are actual pre-approvals- I know they work closely with the credit card companies in creating and managing that platform. Of course a pre approval isn't a 100% guarantee but it's very close in this scenario.
I went there, and the only cards I had pre-approvals for were Amex, which I'm persona non gratis with (blacklisted).
AmEx will show in the "Exclusive Offers" tab if you're matched for any, but if you click the additional categories of your results, you will see other cards you are pre approved for from other banks. The Exclusive Offers category are just ones with above-average signup bonuses matched to your credit profile, but all of the results on there are pre approved.
How long have you been blacklisted with AmEx?