Hi Nishant,
My few cents, there are some problems if you have different ORACLE version because you only can have one ORACLE driver installed in your PI version, i haven't tried the trick suggested by in this thread JDBC Adapter: Deploying Multiple Database Drivers
From multiple schemas i think you can have problems to take the data at once, i think the better approach is to have several scenarios to pick the data and one to merge the data.
Check this note 941317 - XI / PI JDBC Adapter: Known Problems / Incompatibilitiesas well
Regards.