Permissions for revision history
You cannot set specific permissions for revision history – you cannot allow or deny specific users or roles to use the revision history of an item or page. All users that can modify and item or page, are also allowed to use the revision history of this item or page.
To allow a user to use the revision history of an item, you must also grant modify permissions for the item.
This is because, using the Revision history, you can revert an item to a previous version, which is effectively modifying an item.