I have a solution.
A few things were wrong, but the change that finally fixed the issue was to correct the SSL certificates on the two ESX hosts. It seems that the dns names were not resolving properly when these hosts were installed, and the certificates did not have the correct hostnames in the CN entry of the SSL certificates.
Bringing each host out of vCenter, updating the SSL certs, rebooting, and re-adding to vCenter (and preparing and adding into vCD) seemed to fix all the issues. I consider it a possibility that the act of removing it completely and re-adding it could have actually been the fix, but the certificate theory seems more rational given the errors I was seeing the logs before.