Then put it on your old device and activate the sim card. Once that is complete put it into your Nexus 6 and it is finished. The Nexus 6 will not activate the sim card. Even the Sprint version can't activate the sim card for Sprint. The activation payload hasn't been submitted to Google to be downloaded. For example this article of how it works
I hear you but as long as it works right now then it shouldn't be an issue for you. I agree that Verizon probably doesn't want them there and wants you to buy through them so that they can try to get you in a contract for 2 more years. Still though to me getting it to work would be more important than it being in their database cause afaik it doesn't impact the end user right?