first, there is no sync framework 4.
what was supposed to be v4 is now known as the Sync Toolkit.
The toolkit was designed to target new client platforms that cannot install the full Sync Framework SDK such as Silverlight, Windows Phone, iPhone, HTML5, etc...
it is not a version upgrade to v2.1. the toolkit actually requires 2.1 on the server.
so to answer your question, if you want to sync Oracle with SQL Server using the toolkit, you will have to write your own provider for Oracle.
You can also choose to simply use Sync Fx 2.1. Have a look at this sample:
Database Sync: Oracle and SQL Compact 2-Tier
just replace the SqlCeSyncProvider with SqlSyncProvider.