Do hostile foreign countries target highly intelligent people to become their useful idiot dupes?

Beyond your country's febrile politics, it is not as simple as that. Hostile powers seek out whoever is likely to be the most useful for the particular attack.

If they are trying to turn someone working for example in military research or a major financial institution, that individual is one with the appropriate knowledge; so will be highly intelligent and highly educated to have gained such employment in the first place. The security agency responsible will therefore look for exploitable weaknesses other than in learning or IQ, such as a sexual indiscretion, gambling debts or some grudge held. These days too, quite possibly use of unhealthy or even illegal Internet sites. 

If though they are trying to sow fear and division generally, e.g. by false Facebook accounts, they have two choices. They know many will see through their lies, but if they win over even just 1 in a 1000, that is a lot of people nation-wide. The hostile power's account-creators are like fraud gangs in this respect. So they can aim the wilder nonsense at the less educated and more gullible the readers. Or they can be a lot more subtle, sowing doubt by statements that look credible, use improvable negatives, and the like. That can trap people who are more level-headed but might not always question the source and text of a story that looks real and appears to support their views. 

I do not know to what extent such a power also uses personal data that are so horribly easy to give away in spades thanks to the way that Google, Facebook etc. work. At its simplest level it can use the data to aim appropriate political advertising or false messages in the same way as the retailers and their advertising-agencies. Now, an ordinary person's life is not generally important to the political or military eavesdropper, but analysis might reveal useful hints and nuggets such as profession, work location, or exploitable weaknesses.