Not really, it would very much depend on the length of stay.
Someone requesting a visa to teach a course for a few weeks is perfectly reasonable, especially if they are coming from a country with reduced requirements (visa wavier countries) like the EU.
Consider the fact that the only real enforcement of immigration laws happens at the borders here. Once you're in the country, people have (and still) overstay their visas for years at a time. It's very common and one of the most abused rules here.
It's so abused that there was literally an effort (to amend our Constitution) to deny citizenship to children born here from parents who were in the country illegally.
Skilled/unskilled migration/employment is a touchy topic here because many citizens feel like corporations and immigrants conspire to avoid the US employment laws.
I'm not saying it's right; that's just how things are here.
I used to work in London and did so via a student work exchange program. The visa/permit was limited to 6 months and I had to leave at the end, which I did. You may not agree with the laws of the country that you are heading to but you really cant fault them for enforcement. Given that a staggering amount of business is done with the US by foreign visitors it can't be /that/ much of a hassle.
Someone requesting a visa to teach a course for a few weeks is perfectly reasonable, especially if they are coming from a country with reduced requirements (visa wavier countries) like the EU.