The posting written by Andrey Konovalov titled Automate recovery verification of VM backups with Veeam SureBackup is a MUST read if you want to understand the Virtual Lab of Veeam Backup & Replication 5.
The setup of the virtual lab can be a bit complex if your infrastructure has several virtual machines located in different subnets. Understanding of networks is needed for a succesful testing of your backups using SureBackup.
Virtual Lab is an isolated network setup by Veeam B&R running on one of more VMware ESX hosts. It has several purposes. The main purpose is testing of backups of virtual machines. The virtual machines will run from backup storage, obviously using the same IP configuration and hostname as the production server. To prevent conflicts with production servers you will need an isolated network for testing as both production and the virtual machine started from backup are live at the same time.
The posting by Andrey Konovalov perfectly explains the function of the Veeam virtual appliance, networking and scripts!