That's what the DB2 support in SQL Developer is for - for you to migrate to Oracle.
So the DB2 supported platforms on that migration page are also the DB2 platforms SQL Developer supports.
Of course if you want to use SQL Developer to work with SQL Server or Sybase - feel free to. Just don't expect to have the ability to update data, debug stored procedures, or to manage those environments. Running queries and browsing objects - that should work OK.