You can use vCenter alarms that send SNMP traps to vRO:
Automatic VMFS expansion with vCenter SNMP and vRealize Orchestrator | Cody Hosterman
VMworld 2013: Part 2: How to Build a Self-Healing Data Center with vC…
Alternative, you could create a polling workflow in vRO , that checks the vCenter tasks / events.
Searching Events with Orchestrator
Joerg