They certainly would have understood corporate legal status, and done so much better than nearly everyone who comments on it today.
And honestly I don't think it would take most of them very long to grasp the implications of mobile phones, the internet, and encryption. The Founders whose names immediately come to mind were some very intelligent and mentally agile people. While our technology may be incomprehensible to them, the social frameworks into which it fits is not.
The Founders probably couldn't comprehend mobile phones and the internet, let alone modern corporations being granted personhood.
Keep in mind that the founders were some of the smartest, most educated and most powerful people on the fucking planet at the time - Franklin even contributed to our understanding of electricity - so I think that view is not only mistaken but beside the point. They had no need to debate the particular sophistry of our circumstances. The corrupting nature of power was clear to them and we should be thankful that for that.
The constitution also doesn't mention newspapers and the printing press. You don't need to anticipate the future if you're concerned with very simple ideas of liberty and democracy.
They enumerating rights to individuals against the tyranny of an oppressive government and they were very cautious about keeping the government on a short leash and putting that leash in the hands of citizens -- though they seem to think its supposed to be there other way around.
So, who knows.