Our documentation [1] (and my testing) indicates that a serviceAccount other than the default is required to use prehooks during a VM migration in MTV. However, there is no way to specify a serviceAccount in the Console. Presently, we must either set up the hooks via the CLI, or create the hook in the Console, then edit it in the CLI to add the serviceAccount.

 [1]https://docs.redhat.com/en/documentation/migration_toolkit_for_virtualization/2.7/html-single/installing_and_using_the_migration_toolkit_for_virtualization/index#adding-hook-crs-migration-plans-api_mtv