We use hot code upgrades on kosmi.io with great success.
It's absolute magic and allows for very rapid development and ease of deploying fixes and updates.
We do use have to use distillery though and have had to resort to a bunch of custom glue bash scripts which I wish was more standardized because it's such a killer feature.
Due to Elixirs efficiency, everything is running on a single node despite thousands of concurrents so haven't really experienced how it handles multiple nodes.