Yes, as far I know, with Smart IT - in Affected Service field you will see Business Services only. Also, yes - If you create records in CMDB BMC_SERVICEOFFERINGINSTANCE class you will see records in Affected Asset field. That's how Smart IT works.
Service Offerings created in BMC_SERVICEOFFERING class (using Atrium Console - Service Catalog) are not the same - they're used in BMC Service Request Management application (SRD-s)
Maybe you should check some docs/links like for example:
How service request definitions are related to Atrium Service Catalog - Documentation for BMC Service Request Management…
Creating a service offering in the Service Catalog - Documentation for BMC Atrium Core 8.1 - BMC Documentation