Hi Bedwards16,
A couple of things here:
1. When you mention that the domain accounts could not log in, I am assuming that those were the accounts you were trying to access Virtual Center with? The direct host connection using username root and password your password should have worked
2. With Virtual Center 5.1, we have a dependency on Single Sign On or SSO that requires SSL by default. But more than that, if I read the description of the SSL settings screenshot you have posted, I do believe this would only affect the SSL check of the hosts that are connected to VC and the VC functionality remains unchanged.
So 5.1 does not, indeed have an option to disable the SSL because of it's dependency to SSO. But even if the option were enabled, if the VC SSL expires VC service would still be impacted.
Regards
a