Install the DNS-Server service on your vcenter machine. Create a private zone for your ESXi hosts and the vcenter server. At this point the problem goes away.
You can survive without DNS, in that you can survive withour vcenter for a period should it go down.
Even though vSphere 5 now functions without DNS, I really wish it didn't. It's not hard to setup DNS correctly, and it means everything else falls into place.