Hmm, good point. Not too sure about that. I know there's a apk/service thing that can be frozen in Titanium Backup that'll prevent OTAs, so I would assume the OTAs will come through regardless of what carrier the phone is being used on, but it'll be up to Verizon and Motorola to release it.
And yea, $25 for Sunshine for the unlocked bootloader is awesome! Currently running Marshmallow on my Droid Turbo!

(Resurrection Remix ROM)
EDIT: Droid Turbo 2014 users on AT&T were able to get the 5.1 Lollipop update last July, so I assume it'll work once Verizon/Motorola release it.