So, I fixed the issue. Not only does the installer need access to both the host management network but so too does the newly created vCenter server, so I created a new VMKernel port group on the standard switch, and configured the VMKernel port group for management traffic and gave it an IP on the same subnet as the vCenter server. In essence, this creates a new entry point to the host and bridges the vCenter server network to the host's management network!
I completed the upgrade with this change! Thanks all for your help.