Hi Mark,
in the latest development version of Galaxy has support for HTCondor and the Docker-universe. But we still need real world testers :) Have a look at this PR: https://github.com/galaxyproject/galaxy/pull/2278
Recently the Galaxy team also merged a PR which integrates a Kubernetes job runner, see here: https://github.com/galaxyproject/galaxy/pull/2314
So you have these two options. Docker Swarm I would not recommend it is currently not secure and please keep in mind this is all in Galaxy dev and will be released with Galaxy 16.07. I would really like to see some testing before so please get in touch with us if you find problems.
In a related new we also have merged HTCondor Integration into the Galaxy-Docker Image here: https://github.com/bgruening/docker-galaxy-stable/pull/180
So it should be possible to run Galaxy in Docker and submit via HTCondor Docker containers ;)
Ciao,
Bjoern