Hello,
If you do not specify a custom Insert SQL Statement GeniusConnect will generate a default Insert statement.
If an Outlook Item was Added from the database, GeniusConnect will execute an Update statement or your Custom SQL Statement for Update. (GeniusConnect stores the primary key info in custom MAPI fields OCMPRIMNAMES,OCMPRIMVALUES)
In current version, we do not have an options to ignore inserts, You can try to create a dummy custom insert statement without real DB insert.