An update deployment can apply to Windows VMs or Linux VMs but not both. The VMs can be in different regions, different subscriptions and different resource groups.
Update1: VM1 and VM2 only -
VM3: Windows Server 2016.
Update2: VM4 and VM5 only -
VM6: CentOS 7.5.
For Linux, the machine must have access to an update repository. The update repository can be private or public.
Reference:
https://docs.microsoft.com/en-us/azure/automation/update-management/overview