Just getting back in deep with Oracle after a bit away.

Does anyone know specifically what OEM utilizes to connect to one or more various platforms
Varied per platform?

Through OMS or Weblogic, etc...

I've found a variety of whitepapers and documents, they refer to plug-ins, etc... (ex: JDBC for DB2)
But nothing that specifically states it.

Any feedback or insight or direction to potential material would be greatly appreciated.