This integration allows you to develop HaLVMs on a wider variety of platforms, by using Docker as a base. Obviously, unless you have Docker and Xen running together and playing nice, you won't be able to test the things you build directly ... but you can build them, and then potentially ship them off to other machines for testing.
Have a HaLVM / Docker use case? I'd love to hear it. Got any suggestions for other ways we could package the HaLVM? I'd also love to hear that.
If you're interested, the Dockerfiles that we build these image funs are up on hub.docker.com, or available via the HaLVM-Docker repository at https://github.com/GaloisInc/HaLVM-Docker.