Is there any way, similar to how Windows Software Installation policies
work, to have workstation-associated apps show some sort of progress/status
window that overlays (or maybe even inhibits) the Novell/ZENworks login
gina? I've tried setting the apps to show progress, but that does not work.

I think the way this works in the Windows/Active Directory world is that MS
coded some specific stuff for this into the MSgina. I imagine this
functionality needs to be present in the NWgina for it to work similarly?