You should also verify that the DBD::Oracle code (Perl or otherwise...) is capable of being built for 64-bit.   Such modules usually contain “C” code (XS modules...) with low-level structures and other data representations.   Usually, you have to check with the authors on a case-by-case basis.

Right now, we are still very much at a point where “64-bithood is new,” just as 32-bithood at one time was new.   Even though modern processors have 64-bit internal architecture, they still spend a great deal of their time running 32-bit code and probably will continue doing so for many years to come.