Although the term "Dual Citizenship" is commonly used, it is not the case as emphasized by Indian Consulates. However, it does provide for unlimited stay in India and additional rights that may not sit well with laws of some nations. Hence only those that permit a full dual citizenship would recognize the OCI as a limited construct and well within their permissable duality.
But going back to your specific question, there does seem to be some ambiguity within the US-DOS as to how to protect a US citizen who is an OCI when they are in India & have some legal issues. The Website
travel.state.gov states that "The Indian government has indicated that a person who applies for OCI status will not be required to take an oath of allegiance to India. Accordingly, at this time, it is not clear whether an OCI would legally be considered a “national” of India."
Thus, any ambiguity of status puts a US Citizen in harms way and could lead to legal issues, perhaps would not be the best situation, especially if they are prevy to some sensitive information.
IMHO, the safe way is to procure a PIO card that has limited applicability with an expiry date and in essence is a long term visa. Furthermore, it requires registry with Foreigners Registration Officer and thus it clearly classifies the individuals as foreigners. Also there is no parity with NRI in political rights.
Most importantly, there is no confusion about Duality in Citizenship.