I tried making the "obvious" edits to export_descr_buildings.txt and export_descr_unit.txt, but the recruitment viewer showed no changes.
RV doesn't use RTW files.
Its actually the other way around because RV is used in process of creating export_descr_building.

So whatever changes you make to export_descr_building will never be seen in RV.

From what I see African elephants are only recruitable by Ptolemoi,Carthage and Rome.
But in current internal build you can get African Elephants as Saba so maybe they will be available in final 1.1 release.

You can get Indian elephants with Saba though. Conquer Sind province.