Oracle has its own sql database, and sql is a widely used relational database. Apart from this, oracle also has its own NOSQL database ONDB, which is similar to MongoDB.
Hence oracle does use or promote MongoDB since it is technically its competitor. Other companies which are as big as Oracle may choose to use an SQL or MongoDB, but SQL has penetrated the software industry much more since it is much older and has a bigger community around it. There are many more differences between SQL and NoSQL databases that you should read about which makes them suitable for different applications. There are companies that use MongoDB, but again it depends on the type of the application.