...because Oracle.so is 32bit 80386 and perl's libclntsh.so.10.1 is AMD 64

You probably meant "... Oracle's libclntsh.so.10.1 ...".  Anyhow, the problem most likely is that your existing Perl binary is 32-bit, which means that any XS shared libraries - like DBD::Oracle's Oracle.so - built with/for it are (and must be) 32-bit, too.

In other words, you'd need a 64-bit Perl installation in order to link against an external 64-bit library... — or find a 32-bit version of libclntsh.so.10.1.