The reason Beaker checks to make sure the harness repo exists is because Anaconda will complain if we define a repo in the kickstart which is unreachable. But if the recipe is using an alternate harness Beaker could just skip the harness repo definition, instead of complaining.
I guess if any alternative harnesses are depending on libraries we currently have in the default harness repos, they should really be providing their own copies rather than relying on the fact beah also needs them. So +1 for skipping the harnessrepo configuration when the chosen harness is anything other than beah.
http://gerrit.beaker-project.org/#/c/2916/
Getting this into 0.16.1 instead: http://gerrit.beaker-project.org/#/c/2935/
Beaker 0.16.1 has been released.