For Microsoft Azure, Amazon, and other vendors, Oracle does not Certify against 3rd party Cloud Products. (Reference: Oracle Support)
Please read ->
https://blogs.oracle.com/ebstech/post/certification-and-support-for-third-party-productsThis is a good document to understand the Pros and Cons of using 3rd part products in general.
There you will see how oracle certifies its own products and what does it mean to be certified, and what does it mean to be supported.. However, there is a tradeoff in your case.. Having OCI in the picture will make the things a little more complex, but at least your db will be on a certified and supported platform.. Having a non-oracle platform in the picture may mean a limited support...
For instance, we ask how to configure a shared appl top in Azure?
Oracle says : For shared APPL_TOP configurations, contact Microsoft Azure Support in regards to the NFS configuration options with Azure. ( and it adds some reference documents to that..)
But if that system was on OCI Oracle would deal with it on its own, either via a tailor-made support document or on a SR with its engineers..
So please read the document I shared with you above and try to extrapolate using the information you get from that.
These are my comments.. I suggest you to consult with Oracle: Reach out to Oracle to discuss your specific requirements and get their recommendations. Ultimately, the best approach for you will depend on your specific needs, budget, and risk tolerance. Carefully weigh the pros and cons of each option to make an informed decision.
Regarding those third party companies, I don't want to comment.. I don't know anything about them..