Apply logical thinking to the following facts: 1. Apple has very little interest in stopping music piracy, or helping the RIAA to catch pirates. 2. Apple has a huge interest in making money by making you buy Macs, iPods, iPhones and iPads. 3. Apple has signed contracts with the music industry that say exactly what Apple can and cannot do; contracts checked by Apple's lawyers who are not complete morons. 4. Apple knows that people will use iTunes Match to replace pirated songs. 5. Apple knows that if they give information about this to the RIAA, the whole service will be stone dead, and Apple's reputation destroyed, at enormous cost to the shareholders.
Conclusion: Apple will _not_ give any information about which songs you matched to the RIAA or anyone. On the other hand, the RIAA reads MacRumors, and since you are obviously a pirate, they will subpoena your identity from MacRumors and send ninjas to your home who will beat you up. Or worse, send lawyers that take your money, your soul, and your children (or your parents, depending on your age) away.