So after playing with the Moto X and my headset I have learned something more about this topic. On my older phones if I pressed the button on the headset, the headset would prompt "say a command" to which I would respond "phone commands". This would cause my old phones to respond in one way or another, usually just asking me what action I wanted to perform. With the Moto X I have found that when I press the headset button the headset still replies with "say a command" and I still have to reply "phone commands". Once I did this it seemed like nothing was happening until I just blurted out "OK Google Now". At that point the phone is listening to me and waiting for a google now command. This appears to be the only way the phone listens using the headset. Not a bad feature, I just wish I could hit the button and go but this works.
Just a quick update to my post, the one problem I have encountered with using "OK Google Now" with the bluetooth headset is that the phone seems to get confused as to where to route the audio when it does something like read back your text message prior to sending. After using voice commands through the BT headset to tell Google Now to compose and send a text message it then (very loudly) reads the text message back over the phone speaker! Minor annoyance but if you were hoping to do something quietly via your headset you can forget it! LOL