Yes, that sounds like the same issue. I didn't know there is a KB on it. So, that's the fix I was talking about which got integrated into vCD 5.5 and should be in 5.1.3 as well.
Regarding the OS support, it's true that support for "running" those comes from ESXi. With that said, in 5.1.x and before vCD didn't make use of the vCenter API related to the OS support and instead relied on some internal metadata. That has been fixed in 5.5.
The support for "customizing" OSes is a different thing. It's not an ESXi feature. Historically, there have been two completely separate codebases. The one from vCenter and the other one from vCD (which came from the LabManager times). It's only in vCD 5.5 I did the switch to the vCenter codebase. However, vCD still does not call the vCenter API for customization, because the two workflows are sufficiently different.
/Andrii