1 - All voice commands were heard and worked very well, with the exception of saying "OK GOOGLE."
2 - The Google app was different. I came from a Nexus 5 and the Google Now apk when opened, if you scrolled to the bottom, the menu for settings was in the bottom right. That was absent on the OPO version - and I had to go to Google Settings to edit the "OK GOOGLE" recognition / any screen feature.
So... clearly not a hardware issue, which made me feel a lot better.
I then decided to abandon CM11S (4.4.2... with bugs) for a ROM like SlimKat (4.4.4). I also flashed their full GAPPS package.
Low and behold, Google Now worked PERFECTLY. No issues. And wouldn't you know, the settings were at the bottom of the Google Now app. I am uncertain the two build numbers, but I would have to assume one could just replace the Google apk and have some resolution for the "OK GOOGLE" not working.
Below is a video of what I was experiencing on CM11S. Now, this video is making my OPO activate Google Now, just having the video play. Hysterical.
Hope this helps and good luck.