I realize this thread is a bit old by now, but I can personally confirm that the Nexus 6P can be purchased from Huawei or Google and used on the Verizon network with no issue.
I cut my own nano sim into a micro sim (or vice versa) so I could use it. That sim actually just gave out on my a couple weeks ago. The phone wouldn't register it. I took it in to my local Verizon store and they replaced it right away. I was afraid there'd be some issue in getting it activated with the new sim, but there wasn't.
The same should be true for the 5X as well.
I cut my own nano sim into a micro sim (or vice versa) so I could use it. That sim actually just gave out on my a couple weeks ago. The phone wouldn't register it. I took it in to my local Verizon store and they replaced it right away. I was afraid there'd be some issue in getting it activated with the new sim, but there wasn't.
The same should be true for the 5X as well.