You don't think it's even plausible that foreign Cartel drug runners could be considered enemy combatants in light of their goal to flood the USA with illegal drugs which are killing hundreds of thousands of our youth?
No. It isn't plausible. It isn't close to plausible. Giving a foot massage and putting your tongue in a woman's holiest of holies is more closely related.
1. The people on the boat were not enemies. That vessel was not headed to the US -- it couldn't possibly have made it. It was headed to some waystation. Almost certainly the drugs would be unloaded and transferred to another vessel, and the mariners in question would have returned to Venezuela. The drugs might have gone to the US, but they might have gone to Europe, to Mexico, to the Caribbean islands, etc.
2. They are not combatants. And this is an easy question that can be answered without parsing what is a combatant. Just ask yourself this: what would have happened if that boat had been apprehended, say, just outside of New Orleans. The mariners would face trial as drug runners. They would likely serve a couple of years in jail. Maybe the kingpins would serve longer. But even the biggest of all the kingpins, the head boss, the cartel boss, would not face the death penalty. In fact, it is unconstitutional to prosecute drug offenses as capital offenses.
There are hundreds of thousands of people in state and federal jails convicted for running drugs. They are not in special prisons; they are with the general prisoner population. They do not have life sentences. They are mostly serving a bullet or maybe a dime, but not life.
In other words, absolutely nothing about US law would suggest a combatant classification.
3. Contrast with a different case -- let's say the boat contained a working radiological "dirty" bomb and it was apprehended outside of New Orleans. What would happen? First, they would be held in Gitmo, not a regular prison. They would likely be tried before a military commission. They would be charged with a terrorism offense that is punishable with the death penalty -- and indeed, terrorists have received death penalties. So the people running the bomb wouldn't be textbook combatants, but there you could make a plausible case.
But drugs are not dirty bombs. Drugs are not aggressive. Nobody forces Americans to use them. Lots of people actually enjoy them. That's not to say that drug running is good, or that the people who do it willingly aren't messed up, but it's not remotely the same as flying a plane into a building or blowing up an airplane or an office building.