1. Yes, ESRI supports Oracle Spatial (ESRI 10.1 Help- Oracle Spatial). I used both of SDO geometry and ESRI datatypes in past jobs and majority of the time you can't tell a difference. 2.Yes.3. Depends on your needs. Is there a requirement for SDO geometry and Oracle Spatial for other applications? Are you using Oracle Spatial elsewhere? Have you considered using ST_geomerty instead? Does your SDE and Oracle admin know Oracle Spatial or will you require additional training?