There should be no risk on the DWH - The reporting & presentation layer we provide is just one approach for using the data in the DWH - we always intended the DWH to be an API as well, in that the data can be extracted via SQL tools. Some of our customers eschew using the presentation layer entirely, as they do reporting in their own tools, or bought OCI to feed other products, like billing systems
From your first post, it sounds like you were look at the legacy SOAP / Web services API. We are intending to eventually eliminate that, but it will take a long time. We are not adding new features to it.
OCI 7.0.1 and high has a REST API - this is good for interacting with the performance data OCI collects, if you need it as the same granularity the OCI UI presents.
We don't have out access to the OCI operational database - it is optimized for performance, not for human legibility. Conversely, we generally expect OCI DWH schema changes to be additive over time.
Generally speaking, CMDB uses cases line with with the OCI DWH well - you are not looking for real time data, working with SQL is a plus, and it acts like a consolidiation point (OCI customers with > 1 operational OCI instance would need to work with the SOAP / REST API on each OCI instance, whereas 1 OCI DWH can consolidate multiple OCI instances into a one stop shop
Matt