More and more storage vendors are certifying their stretched cluster solutions. Recently NetApp and IBM have both been added to the VMware HCL. Below you can find the links to the KB article which describe the supported configuration and the tested scenarios.
Those at the point of deploying a stretched cluster I would highly recommend reading these KB articles. Get as familiar as you can with the failure scenarios described, test them over and over again. This is key for operating a stretched cluster and will also give you a deep understanding of how your environment responds to failures.
