* People who love RDBMS technology. Oracle's Database division is big and has a lot of veteran and very skilled software developers and architects who work with the Database kernel code. New employees can also work on this code. I am sure a lot of people would like to work on the database kernel with skilled and intelligent teams. RDBMS as a domain can be fascinating for developers. It involves everything from compiler design (SQL) to system programming (memory management, locking semantics, concurrency, etc.)
* People who love to work on open source and get paid well. Since Oracle ships its own Linux and since the database is also certified to work on many Linux environments (not just Oracle Linux), Oracle takes the responsibility of patching security problems in the supported open source environments if the upstream does not patch in time. A lot of people like this kind of work where they can work on open source, security and development at the same time and get paid while doing so.
* System programmers. Many developers working on the Oracle Database are involved in system programming.
Disclaimer: I work for Oracle.