Bottom line - no one here reported ever "getting caught," so while I cannot officially condone it here in writing, it does appear that as long as you use good judgement they are not going to "sniff you out."
That being said, if you start chugging straight from a bottle of "Jack" with a WalMart price tag on it while you are sitting by the pool, they will probably take it away. And I don't think putting an umbrella in it will fool anyone!
I don't smuggle booze on board, because i don't care to drink alone in my room. So, if I were to drink it would be in public and I would buy it from the bar.
I do think the majority of people who get "plowed" and obnoxious probably also are the ones sneaking the most booze on board, so I don't really disagree with the policy.
If there was a way for carnival to say, "Hey man, it's cool, just keep it real" they would. But some people always want to push a good thing too far, so they can't.