If an IP is assigned manually from subnet reserved for vRA deployment it causes IP conflict because vRA remains unaware about this assigned IP.
Can this exclusion of IP address achieved using vRO workflow or Extensibility ?
Can anyone suggest the solution ?
You may be able to achieve something using extensibility but it would be very clunky. You would be better of using a dedicated 3rd party ipam solution, for example InfoBlox or PHPIPAM, as they will scan subnets and reserve addresses that are found privately assigned within a scope. Most IPAM solutions can be integrated into vRA with either a plugin OotB or by writing an interface for it.