Tableau uses the SAP OLE DB for OLAP provider (part of the Open Analysis Interfaces) to interact with SAP BW.
If you need more details, we have a knowledge base article that addresses the driver question in more detail as well as several other commonly asked questions:
Thank you Sankar,
Is there any difference in working on a Windows 7 or Windows 8 machine?
This is technically not correct in regards to SAP BW. What you have on that link is a link to SAP's support site. In order to actually get the drivers you need to have an SAP support account. There may be files actually stored on that link, but SAP BW is not it.