A quick Google suggests HPE Greenlake is an on-premises cloud-ready computer hardware solution. So as long as it is running SAS-supported processors and OS then SAS 9.4 will run. SAS Viya is primarily a public cloud offering, although AFAIK there is at least one linux-based on-premises option.
Yes, HPE GreenLake now supports SAS Viya on-premises. HPE, SAS ad Red Hat have created a joint solution for SAS Viya. The technical paper is available at: https://www.hpe.com/psnow/doc/a00138240enw
This paper describes the solution for virtualized SAS Viya using Red Hat OpenShift using hostel control plane. HPE ahs also tested VMware based Viya deployments: https://www.youtube.com/watch?v=x2XJ9a7QxOI
The SAS Users Group for Administrators (SUGA) is open to all SAS administrators and architects who install, update, manage or maintain a SAS deployment.