OpenODS is not, by all means, required to implement BW. It's an option.
The HANA EDW concept (where the BW modeling paradigm is the core component, together with HANA native SQL modeling) is all about giving options to the modeler, to best adapt the model to the actual business requirements. And the OpenODS is the provider you'd use when you want to build the logical data warehouse concept within BW with data coming from external databases that you don't want to persist either in BW or native HANA.
If you had data residing in native HANA, you don't even need the OpenODS, just create an information view (analytic or calc view) on top of your tables and you can directly include that HANA View within a BW Composite Provider.
Regarding the picture you mentioned, the "Open Operational Data Store layer" is not exactly similar to OpenODS. OpenODS is a provide type that is available within the new Operational Data Store layer in the LSA++ concept of BW 7.4+ on HANA. It includes the OpenODS, regular DSOs, w-o DSOs, etc.
For real-time reporting with ECC as the Data Source, you don't need to use OpenODS necessarily. Again, OpenODS is for not-persisted data that reside outside BW but that you still want to include in your models. For real-time reporting, you can use the new ODP-SLT data source (check page 28 of the same document).
Best,
Henrique.