That would be a NO!! unless they have changed things in the past 4 months. You might find a shore excursion that will allow you to do this. Everything that I have from carnival says that you need to bring your certification card with you.. hope this helps
Rick, no you cannot get certified on a Carnival cruise. They do have excusrsions for certified divers, (bring your PADA card as they check), and they also have a intorduction to scuba diving where they give you a brief lesson and certified instructors take you on a shallow dive.