If you have renamed HyperV Hostname and Veeam cannot connect to enumerate the VMs running, use this script to change the hostname of the HyperVisor:

Asnp VeeamPSSnapin
$server = Get-VBRServer | ?{$_.name -eq "IpOfVC"}
$server.SetName("NewIP")

This will rename the host from the existing in Veeam to the new one you have set.  No reboot required.