I had seen what might be a related problem a few weeks ago with a host, and reinstalling the OMSA agent fixed it for me. My inventory was failing, and so was the host part of the test connection profile, and rebooting the host didn’t make a difference. I don’t recall if the iDRAC credentials were passing or failing, but I think they were passing. I knew my host credentials were correct so I went to the host console, enabled troubleshooting and removed the OMSA agent using the esxcli (rebooted afterward). I then had the integration’s Host Compliance wizard reinstall the OMSA agent (required a reboot). After the integration completed installing the OMSA agent, it came up compliant, inventory succeeded, and my test connection profile worked. Unfortunately I didn’t take the time to investigate further while in the broken state and didn;t make note of the OMSA version that was on the host. This may not even be your issue, but something to try as the problem appears to be isolated to this server. For further reference, could you post what version of OMSA agent you are running on your T310?
I have upgraded from 1.7 to the 2.0 plugin and having trouble with one host (T310/ESXI 5.1u1).   The connection profile test fails for both the idrac and host although I *know* the login credentials are correct as I can log into the idrac6 express (web login) and the esxi host (web, vsphere client, vcenter).  This used to work on the 1.7 plugin for a bit but I even tried switching back to the 1.7 version and have the same failure now too. My T620 with the same credentials and in the same connection profile work just fine.  I just can't get the T310 to go.  I can't even read the rest of the error on the connection profile test screen (can't expand the window or seem to find the error in the log tab on the interface). I've google'd till my eyes are blurry and can't seem to figure out what is wrong here.  Any help would be appreciated. Thanks in advance
Stumped with Connection Profile errors for T310