On the VMware ESXi 5.0 Reference poster there is a nice table that references vCLI commands to PowerCLI cmdlets. There you can see that the vifs.pl script relates to the PowerCLI Copy-DatastoreItem cmdlet.
There is not a good PowerCLI equivalent for the esxcfg-volume.pl script. You have to call the vSphere API's using the Get-View cmdlet.
To list and resignature volumes you can take a look at the scripts presented in this thread:
Enable Mount and resignature of snap luns on vSphere.
Regards, Robert