Hello Tim,
my second thought...if vCSA is stuck at checking for updates from "external" sources (stubborn to use URL source) it might be worth a try configuring it
for zipped update bundle (Use Specified Repository).
See:
vSphere 5.5 Documentation Center
http://www.virtuallyghetto.com/2013/05/how-to-create-offline-update-repository.html
Regards,
P.