How can we invoke vRO Workflow without vRA.
Can we duirectly start vRO workflow from via or Incident ticket ?
To launch a workflow from an external system, you can use vRO REST API.
Check the documentation available on vRO appliance; for example, docs for vRO REST execution controller - https://{VRO-ADDRESS}:{VRO-PORT}/vco/api/docs/index.html#/execution-controller
There is also a tutorial by Burke Azbil - https://www.vcoteam.info/articles/learn-vco/268-how-to-use-the-rest-api-to-start-a-workflow.html
Aside from the REST api there is also the Cloud Client. Gives you a CLI which you can also script to. There is also this project https://www.helloitscraig.co.uk/2016/08/vro-powershell-powervro.html for calling vRO from PowerShell if thats your thing.
Paul