There is NO out-of-the box integration between Ariba's SiPM module and SAP or SAP Master Data Governance (MDG).
Ariba offers out-of-the box Web Services to export/import Supplier Profile Questionnaire information. These Web Services have delta extract capability - i.e. they will return any supplier record that has been modified within an inputted time range.
You will have to leverage a middleware platform (ex. SAP PI) to schedule these web service calls to pull supplier information on a recurring basis. You then will have to custom develop/leverage standard services on the ECC/MDG side to either create the Vendor directly, or create a Change Request (in the case of replication to SAP MDG).