All nexus devices have an unlockable bootloader and are rootable. Even if they are purchased from T-Mobile, Sprint, etc... Google makes the device and then sells it to the carrier and that's why they are not carrier branded and bloated.
Nexus devices don't receive updates from the carrier themselves, the updates are pushed straight out and are updated by Google. That's one of the main benefits of owning a Nexus device, its a developer phone and is actually one of, if not the easiest devices to unlock the bootloader on, root and plus these devices have a very large development community. Google makes the Nexus devices and then sells them to the carriers... That's typically why when you purchase one from a carrier it will cost you more (like $100 more) than what what you can order it from the playstore. Plus Google doesn't discourage or void warranties for Nexus devices with unlocked bootloaders or for being rooted.