A Document Type, that should not be visible to the Vault user, is visible during classification.
The Create Document permission is granted on a child Document Type that is defined under the affected Document Type.
Granting the Create Document permission on a child Document Type also grants view access to its parent type during document classification in Vault. This is because the parent Document Type needs to be selected before its child Document Type can be selected during document classification.
Vault Admin Documentation: Configuring Document Types