NRI's can give CET (they are indian nationals), CET=> common entrance exam, PIO/OCI who are foreign nationals can not.
(NOTE AP just started allowing PIO/OCI to appear for this exam in 2010), other states do not.
So NRI and OCI are not exactly the same... I too have read the "parity with NRI" statement. This is a very generic statement.
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Here is Info from MHA to AMIT SIKKA RTI regarding" parity with NRI":
http://www.rti.india.gov.in/cic_decisions/WB-13032009-01.pdf
I would recommend searching other sources for this too.