How can we invoke vRO workflow without calling them from vRA.
Can vRO workflow invoke via EMAIL or Incident ?
vRO has a REST API which you can use to invoke workflows
Also, some plugins (such as the AMQP plugin) can be used to trigger a workflow based on an event using a vRO Policy
Lastly, I have in the past written a workflow to run on a schedule which polled a mailbox, retrieved mails in a specific format and triggered a workflow to execute based on the mail content.
It really depends on what your requirements are tbh