Yes, others have reported that Play Store N6s worked with a Verizon SIM. The tricky part is getting activated. If you already have an active micro SIM (cut down to nano SIM size), or a nano SIM then it's plug and play.
But if you need a SIM card you'll have to convince Verizon to cough one up. Some have had limited success getting one from a Verizon store, but Verizon is pretty stingy with them.
Also you may have to call customer support to get them to add your IMEI to their database, as sometimes there's problems activating a new SIM on a non-Verizon purchased phone. Though the problem seems to be on Verizon's end, since the Nexus is designed to work everywhere.
In all, every N6 sold in the US should be compatible with all the other carriers. Sprint seems to be the biggest stickler when it comes to coming from other carriers, but all the others should work by just popping in an activated SIM card.
But a lot of this is outside my personal experience, and I'm just stating what I've seen others have to go through to either activate their phones, or move to other carriers. I just bought mine right from the Verizon store the day after it was available. So upgrading was a nonchalant affair for the most part. And the phone was already activated by the time it was in my hands.
Still, the fact that I could take it to another carrier with just little fanfare (for the most part) is simply fantastic!
For further information on the subject you might want to read these links about activating the N6 on Verizon when purchased through other sources:
https://www.reddit.com/r/nexus6/comments/2t51je/finally_got_my_nexus_6_activated_on_vzw/