Legally, it depends. The term you're looking for is "criminal conspiracy". In US law this is, roughly, an agreement between two or more people to commit a crime, and at least one of the people commits an "overt act" in furtherance of the crime. In the case of these officers, and in your two hypotheticals, there is an overt act taking place. An overt act does not need to be illegal, it just has to be an action taken to assist in the planned crime. For instance, buying ski masks is perfectly legal, but if you bought ski masks in preparation for your bank robbery, that counts as an overt act. But is there an agreement to commit a crime? Generally speaking, in the company-offering-services example, if you did not know the other party was going to commit a crime, and a reasonable person in your position wouldn't think the other party was planning to commit a crime, you are not engaged in criminal conspiracy. There's tons of special cases and nuances here, but that's roughly what happens.

That's if they charge conspiracy in the first place.

The more general answer here is that the criminality of exploitation depends a lot on your state of mind (a property of law that something HN always has a hard time with). A professor teaching a class to an anonymous group of students is not at all the same thing, in criminal law, as that same professor standing behind foreign intelligence operatives coaching them on a targeted attack.

The confounder here is that there are statutes you can theoretically violate by providing some specific exploitation tools to foreign nationals.

The MIT professor, in an MIT classroom, is never going to be charged (same almost certainly goes for a consultant teaching an exploit class at Black Hat USA).

Let's say you are a gun instructor. You take your student out to the street, hand them a sniper rifle and point at their victim. You walk them through the process of pulling the trigger and how to make sure they get their target.

The judge isn't going to let that slide. In both cases, you are an accessory.

Technically I think both parties would be guilty of murder, but that's specific to murder charges. For instance, getaway drivers have been charged with murder because the robbers they transport shoot someone.

That is specifically "felony murder", which wouldn't apply here (though conspiracy might?). Felony murder is the idea that you are guilty of murder if someone dies as a result of you committing another felony (sometimes from a specific enumerated list).

If you are a direct participant in the murder you might just get charged with it (perhaps as a conspirator which I think often has roughly the same penalties).

How many School of the America's instructors were prosecuted?

Strictly ethically speaking, yes they would be at fault