Federation is just a parameter on DB2 database manager level which when enabled will allow the capability to access other databsaes (through user mapping, create server, nickname etc.). But again as I said earlier DB2 software without DB2 Information Integrator (Oracle wrapper in this case) will not allow one the capability to acess Oracle database or as a matter of fact any non-DB2 RDBMS.
Federation has to be enabled to access "other" (DB2, Oracle, Teradata etc) databases but for non-DB2 databases DB2 II is the way to go, unless I had not catch up the latest technology advancements
http://www-306.ibm.com/software/data/integration/