They can't seed it while creating the AMI. If they did that, everyone would share the initial seed and I could boot up the published image, run the generator with that seed, and be able to predict (for example) what ssh key your server will have.
(Or if you meant creating the VM, as explained before they can't do that for encrypted volumes for example)
(Or if you meant creating the VM, as explained before they can't do that for encrypted volumes for example)