I believe the server generated option is done by your mobicontrol deployment server. They usually look something like

{73E65B76064901080003-1BF03A370600}
I recommend using the "ID created by manufacturer" option personally. I find it easier to manage licenses that way, as wiping and re-enrolling a device reuses the already existing device in mobicontrol, where server generated ends up creating a new identifier, and can result in you having multiple instances of the same device in your deployment.