The solution is to clear the cache where NAC/Netsight stores the virtual router names.
Go in OneView to administration, diagnostics. Enable Level Advanced, select System/Network Monitor Cache and select Remove Device. Insert the IP of the switch and click OK.
This will clear the stored virtual router name and should discover the correct one now.
If the problem persists, you can prevent Netsight from fetching the wrong information again by changing the CLI credentials for the switch to a not working one (Netsight uses CLI to fetch virtual routers names), then correct the virtual router name in NAC and correct the CLI credentials again.