"The other array is IBM Flash System A9000R (it is still in Soporte as a specific case, but officially IBM has called it as EoL/EoSL). I think it doesn't run Storage Virtualize."
If you have an A9000 it cannot natively replicate with a Flashsystem the only option you would have is to virtualize that A9000 with either a Flashsystem(5300, 7300 or 9500) or an SVC. Any of those options would require virtualization licenses but depending on the size of the A9000 it might be cheaper to just replace it with a new flashsystem. The other option would be to do it through software (hypervisor or on the application layer).
"When you say - IBM array from another vendor, do you mean any 3rd Party Array can be a DR Target. Possible?"
Sorry I meant to say Array from another vendor and not IBM array from another vendor. Any third party vendor can be virtualized by a flashsystem (5300, 7300 or 9500) and then that combination of Flashsystem+Other Array can replicate to another Flashsystem.
"And once we do the External Storage Virtualization, how can we make it seem like a 'Replication' or some kind of a DR setup. Does there exists some kind of copy services in this case. Or, can we use 'mirrored volumes' concept of FS7X00 to get into REPL/DR thing."
After you virtualize the external storage you can treat those volume like you would all the local Flashsytstem volumes, you can replicate using either legacy Metro Mirror or Global Mirror or the new Policy based Replication, it will all depend in the version of Storage Virtualize you are running on the Flashsystems at each site.
"On a different note: We also have a totally unused licensed - IBM Storage Scale Data Management Edition. Can it be used along with FS7X00 to provide a DR solution. Thanks."
Unfortunately not, Storage Scale is a File/Object Storage solution while the Flashsystems are block storage systems.
Hope this helps,
Regards,