If you are asking whether it is necessary to manually execute sysprep from within the Guest OS when using the Customization Specification and a Template; it is not required. When you deploy from template using a customization spec, the VM will boot up, "customization" will begin, sysprep will be called automatically in the background, and the VM will reboot. Five to 10 minutes later, you will have a sysprepped VM.
If you are deploying 2003 or XP, you have to copy the sysprep files for those OSes to the vCenter Server for this to work. For newer OSes, it calls the built-in sysprep in the Guest OS.