A few sources disagree:
http://www.ibtimes.com/apple-homekit-devices-wont-include-go...
> "Apple’s MFi guidelines require manufacturers to use only Wi-Fi or Bluetooth, and also include a specialized chip for authentication"
http://www.digitaltrends.com/home/everything-that-works-with...
> "The certification ensures that these smart home devices have an authentication chip and have undergone rigorous testing to get Apple’s official seal of approval"
http://www.eetimes.com/document.asp?doc_id=1327267
> "Apple Inc. requires anyone making a device compatible with its HomeKit environment to buy and use a special identity chip."
Now, I don't have access to the official docs for MFi - so maybe these sources are all wrong. But I'm pretty confident a special chip is required.