The Nest WiFi Router needs to connect to the internet through an Ethernet (wire) connection. If your cellular hot spot device has an Ethernet port, a Nest WiFi Router might work. If not, then you would need another piece of hardware to act as a WiFi client (to the hotspot) that does have an Ethernet port the Nest WiFi Router could use. I don't think I'd recommend that configuration for anything other than a temporary situation.
I just wanted to jump in real fast to see if you saw MichaelP's reply and to see if you still needed some help on this or if you were able to get it sorted out. If you are still needing some help, just let us know and we'll be happy to continue helping.