I’m having a look at the source code of OracleSpatial10gDialect and OracleSpatialSDO10gDialect and I don’t think they are properly serializable. The reason for this is the sdoSupport field is marked as transient but it is assumed to be non-null in various methods and never set in a #readResolve method or similar.
Also OracleSDOSupport.isOgcStrict seems unused.