Management commands are the same as django management commands. They only run locally from the command prompt.
There's no need for any handlers for management commands, they don't run on production servers, and they don't run in response to HTTP requests.
EDIT:
cron.yaml simply specifies a url to call on a scheduled basis. You can treat that url like other urls. Here's an example where the cron calls are treated like other calls, but take advantage of App Engine's authentication to make sure random people are not accessing it. In this case, the request will still get routed through django's request handling, and you'll have to add the appropriate handler to urls.py:
- url: /cron
script: djangoappengine.main.application
login: admin
- url: /.*
script: djangoappengine.main.application