Not sure why you're confused since vSphere is a different product and nowhere on that linked page does it even mention Workstation! The page you linked, vSphere Management SDK for vSphere 5.5, is for vSphere not Workstation.
What is available that can be used with VMware Workstation is the VIX API although it's quite limited compared to what vSphere Management SDK offers for VMware vSphere.
Depending on the level of automation you're looking to accomplish with VMware Workstation it may take a combination of the VIX API and Scripting along with... Using vmrun to Control Virtual Machines