Two numbers are not enough to identify a location. ArcGIS geometry objects include spatial-reference information, with wkid and sometimes latestWkid describing the reference system.
For the ArcGIS integration, keep that information with every geometry. Test a known landmark before plotting a larger dataset, and verify any requested output reference. Treating arbitrary x/y values as longitude and latitude can produce plausible-looking but completely misplaced results.
Akousa