it depends on yourself. If you want to attend a school, you have to make
sure they give your some experience and real world senarios. You can
read the docs from otn.oracle.com. The more you practise, the more
you get experience. Certificate is not a big issue, employer more
concentrate on experience. You have to know system environment,
such as UNIX environment, storage management, database configuration, backup strategy,network, etc...

Oracle dba is easy to get in than UNIX admin. It is more logic
thing than unix which require you to know hardware, cabling things.

You 'd better starting from a small company and simple environment.

hope it is helpful to you.