Well, you have a challenge to resolve host name, means DNS is not working on the system you are trying to run the installer on.
We don’t have a docker imager as it’s doesn’t make really sense to create a DietPi system in Docker. Because the whole configuration of a Docker container would need to be done before the container is created. Means you already need to define all ports and directories you like to have on your container. If you go to install some apps later on, they might not be reachable as the port is not defined on the container and you would need to create a complete new container.