And like I said, I am not 100% sure on the casino part either. I have pulled money from the S&S to play video poker (since there is no 3% fee fro adding money on a slot or video poker machine) but the other charges on my S&S account more than used up my OBC amounts anyway. BUT the casino is operated independently from the ship so I don't think you can use it for casino cash (unless maybe if it the fully refundable kind of OBC).
Don't worry about it. Like I said, its rare that you would pull in enough in OBCs to fully cover a S&S bill.
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise
NCL Dream October 2006, RCCL Mariner OTS June 2007, Celebrity Silhouette 2013