is BigIP capabale of providing auomatic site failover for SAP HANA? Has it been tested and validated for such failover solution?

At a high level, GTM should be able to give you DR failover capability. GTM would handle this through DNS and health monitoring. Depending on your setup though, this function could also be handled by LTM.

If you'll elaborate a bit more about your environment, a better recommendation could be made.