A fiend of mine in Florida who is using Zello told me it works off of cell and wifi signals only. No RF involved, unfortunately. She also told me that Comcast is expanding their hotspots and suspending usage and data charges for the duration of the storm. Unfortunately, towers and hot spots need power and after battery backup is exhausted it means that comms will eventually go down with or without this app.
"If I'm gonna die, I'm gonna die historic on the Fury Road."