Odata is an open standard, and SAP's recommended way of developing mobile app is using Odata protocol to access the data from backend. It allows access to different data sources in a common way. The native SDK that comes with SMP 3 is based on Odata, it provides open and flexible way of developing online and offline native applications. The native SDK is common for on-premise and cloud version (HANA cloud platform mobile services) of SMP. Currently Native SDK supports iOS, Android and Windows.
The SDK can be installed on a developers machine, it supports Windows and Mac.
What if the protocol is non Odata?
You will not get the advantages of Native Odata SDK like offline, Push Notifications etc. But you have the option to convert non Odata protocol to Odata protocol using Integration Gateway that comes in SMP 3.