I am also doing separate NICs on my vCenter server to separate the ESXi management network.
I had issues with host disconnecting 60-90 seconds also and it ended up being an issue with Windows firewall so you may want to double check that. If you joined vCenter to a domain after you installed the vCenter server you will need readjust you Windows Firewall settings.
Also note that to be able to access VM consoles through the vSphere client you have to provide a route to and from the management network through the vCenter server.
Besides that it has worked well in this configuration.
Hope this helps.
Hersey