As of now, if we want to query ArcSDE Geodatabase which stored in Oracle, We have the following ways
1) Query using ArcObjects classes
2) Query the GeoDataService if we have ArcGIS Server.
3) Query using REST or SOAP API s (If our data is published using ArcGIS Server)
By all the above methods we cann't Query Oracle tables directly. and these are little bit time consuming if geoemtry is complecated.
Instead of with these methods if there is a direct way to query Geodatabse(In oracle or SQL Server) tables using st_geometry functions it will be fast. Actually this method is possible using Oracle.DataAccess.Client library. But we have to implement a CustomMapping class to work with st_geoemtry. If it is possible please implement an custom interface to work with SDE directly with out using any ArcObject classes or an SDEDataAccess dll like oracle dataaccess dll.
Thanks and Regards
V.Srinivasa Reddy