Publishing Code Coverage Results from ReportGenerator not working
Well, in standard operating procedure, get annoyed, write a long post on Stack Overflow, find a nugget somewhere, and solve your own problem.
It is not a parameter, but rather an environment variable that needs to be set. Adding the following to the start of the Yaml file takes care of it.
variables: disable.coverage.autogenerate: 'true'
Leaving this here to save the next person stuck on this problem days of trouble shooting. :/