The only thing that's not available is developer portal content. Everything else is available through ARM.
Check out this article, if you use a private repo, you can add a step in your pipeline to copy the linked templates to a blob container and access the files with a SAS token.
If you are trying to make multiple changes to the same API (e.g., import an Open API definition, add to a product), then you should daisy chain the operations using the DependsOn element.