I want to fly on a domestic flight in India. Is it enough to have my US drivers license or do I need my passport w/ OCI?
No, your US or for that matter drivers licenses from any other foreign country aren't valid to board domestic flights in India. Here is the information from the websites of Air India and Indigo. I suspect you'll find identical information for other airlines too.
Passengers are required to ensure that they are in possession of all documents necessary for travel, apart from their tickets. For domestic travel within India, valid photo identification, namely
PAN card issued by the Income Tax department,
Election Photo Identification Card,
Valid Driving License,
Photo identity card issued by the employer, being government and reputed private sector organizations,
Photo Credit Card,
Children should carry their school identification cards or any other photo identification proof,
Valid birth certificates of infants,
For travel under Concessionary fare types valid relevant IDs.
In case the Customers do not possess any of the above documents, they should carry a relevant attested document that contains a recent photograph of the traveling Customers.
For Foreign Nationals, the only valid photo ID for travel is Passport.
Considering how many different Driver's License types the US alone has, you can hardly expect that some official in India is familiar with all types of all Driver's Licenses in the world, so he would not be able to differentiate between a Driver's License and an Health Club Membership or a self-printed laminated fake.
That implies it is not sufficient.
However, considering the way things are handled in India, there is always a chance that he has seen them before from just that state, and maybe you can talk him into accepting it, for an extra 'fee'. I would not rely on that, though.