Be aware that the latest ESXi ISO files supporting ProLiant Gen8 servers are now on www.vmware.com and not anymore on the HP Software Depot.
Follow the steps below:
1. go to www.vmware.com/download
2. Select vSphere
3. You will see Product Downloads/Drivers & Tools/Open Source tabs. Select Drivers & Tools
4. Expand the OEM Customized Installer CD section and you will find it there.
For other files, go to http://vibsdepot.hp.com/