What do you mean by "can PL/SQL code be implemented in perl"? Do you mean can you make a perl-ish translation of whatever your PL/SQL procedure does (most likely yes) or do you mean can you put your PL/SQL procedure's code in perl have have perl set it up and execute it? (again yes.)

The DBD::Oracle perldoc has PL/SQL examples of the latter.

Personally, I prefer to have the Oracle DBA be responsible for loading the PL/SQL procedure into the database. Then I can easily call it from perl without having to ever worry about it. That way if anything goes wrong, I can blame the DBA :)