It depends on how the virtual disks are provisioned. With thick provisioned virtual disks you could just copy the VMs (powered off) using e.g. FastSCP. However, I'd personally prefer to backup the VMs using an image based backup application and restore them on the new hosts. This will not only be a save way to do the job, but also allows you to keep a backup of the VM's current state. Unless you have a backup application, take a look at e.g. VeeamZIP (for licensed ESXi editions) or Trilead's VM Explorer (in case you are running the free ESXi Hypervisor).
André