Of course, Oracle has so many different software offerings (duplication due to acquisitions, and lots of industry-specific offerings), it couldn't possibly use them all internally. But at least its sales reps could say, that if they weren't using the specific product they were selling, they'd be (for non-industry specific functions) using an equivalent product in Oracle's portfolio.
Amazon themselves say it is true: https://aws.amazon.com/blogs/aws/migration-complete-amazons-...
Although note this small print:
> Amazon’s Consumer business just turned off its final Oracle database (some third-party applications are tightly bound to Oracle and were not migrated).
No idea what those “third-party applications” are and how significant they are - they could be insignificant fringes or extremely core business systems (such as payroll or general ledger)
Probably they've migrated off now, but IIRC they've used PeopleSoft, because of course it is.
So, Microsoft's own Dynamics offers no greater value than their competitor SAP, even within ... Microsoft.
[0] Recent example - https://www.oracle.com/cloud/oracle-at-oracle/ - although they were saying similar things 15 years ago, albeit minus the cloud part