Do you know you're having a problem or just looking out for them?
The code for JDBC should be the same between servers, that is the way it is designed. The only difference I can think of is that Oracle give their classes additional methods, available through casting to the correct type. Not really advisable though.
Artemesia, Not specific to PreparedStatements, but make sure you aren't using any SQL server or Sybase specific SQL statements. Oracle uses standard SQL, so you will be ok if you didn't use any specific extensions.
I agree with the previous post. I use PreparedStatement with Oracle all the time & it works just fine. Of coruse, if you're porting queries previously used in other RDBMS's, you'll need to ensure the SQL doesn't have any proprietary (i.e., non-standard) extensions.