Just answering the basic question of "Can they be rigged?" I say yes. What proof do you have that it contains six FULL decks of cards? What proof do you have that some ten valued cards were pulled and replaced with low cards? I guess on land the gaming commission can do surprise inspections but who regulates the cruise ships?
I was on a Carnival cruise last September. I played every single day along with several other passengers who were regulars at the tables every day. I not only watched my own hand but the other regulars as well. We all played excellent basic strategy. We hit, stayed or doubled whenever called for. Of course the house still has a small edge but it would take them a long time to chip away at your money.
I strongly believe that they had some ten value cards removed from those machines. It was almost suicide to double down. The dealer rarely busted on an up 5 or 6 card. And if you got a 19 or 20 it wasn't unusual for a push. The other players and I would just look at each other in total disbelief. And this was not just one evening or an isolated run of bad luck. This happened all week long.
In February I was on another cruise with a different cruise line. Thankfully the tables were all hand shuffled decks. I played all week on the same stake and cashed out with a profit.
I know that wasn't your specific question but the CSM's can be "rigged" as far as I'm concerned.