Possibly. If not you can always take the sim out and check for update over wifi. That would work. Something like this happen with the Moto X Pure Edition where cdma carriers got marshmallow first then GSM carriers got it but the work around was to check for update over wifi
That said, how are updates handled? By IMEI correct? So if and when Verizon pushes an update, a Z Force Droid on AT&T should still get the update, correct?
Yep. Verizon doesn't push updates - Motorola does.
source? has it always been this way?