You should be able to just cut the SIM, if you do it right it will work. They can activate it for you, you just have to have the right person do it. It won't be recognized, that's true, but it can be activated. It's much easier if you already have an active nano SIM to pop in but since you don't you are at the mercy of whomever you happen to get helping you.
Verizon will probably never recognize it so you're going to have a few issues with it. If you are getting the $15 or $25 per month savings on a More Everything plan off contract that will go away. I've read where it can be credited back with a phone call to CS but it won't be automatic. And who knows how long they will play the credit game. Also, you won't be able to make changes to your plan/account, at least on the My Verizon app. Maybe you can online, not sure about that really. You'd have to call CS and deal with them. Also also, updates won't come to you OTA directly from Verizon. You can side-load and/or root. All of that is moot though if you are not staying with them.
I really, really tried to like the Nexus 6 but it wasn't the phone for me. Even if it had been I'm not sure I would have jumped through all the friggin' hoops to make it play nice with Verizon. Of course it's much easier if you get a Verizon branded phone but that's not the whole point of the Nexus 6. Stupid Verizon, I hate them for so many reasons yet here I am with them.