Hi Marin,
Integration gateway in SMP was introduced to solve two problems.
- To convert non odata protocols to odata protocols, hence the mobile apps created on SMP 3 will get all benefits of the platform.
- To mash up different data sources - You can create an odata service that connects to different data sources, it is also possible to create a single odata service from multiple existing odata services.
If you have an SAP gateway it is not needed to use integration gateway unless you need to mash up the odata services ( SAP gateway- you can install it as an add-on on existing ERP or keep it as a separate server)
If your backend is SAP, it is recommended to use SAP Gateway.
Regards, Midhun
SAP Technology RIG