Yes, users can log in to one Zello Work account on multiple devices, but the account can only be active on one device at a time. 

For example, you can log into Zello Work on both your computer and mobile device; you cannot, however, be logged into those two devices simultaneously. Logging in on one device will prompt a logout on the previously in-use device.

You'll receive a banner notification if you're logged out on one device. 

iOS	Dispatch Hub

While this means multiple users can share one login account, they cannot be active at the same time.

Tip: Check out this support article for more information on instituting Zello’s shared devices functionality.