After booting RHEL5 into rescue mode, a very limited environment is brought up and ususally the user would chrott to the install image to fix his installation. It though would be helpful to have tools like vgrename available from the rescue image in order to change the system images lvm2 settings, which is not possible once it is activated.
They are there as they're just different modes of the lvm command. lvm vgrename, etc.