I think I am getting closer, but the problem is still with the WHERE clause on the view. It is not possible for the users to create a where clause like:
where DECRYPT_TEST(empid, 'zzzzzzzz') in (1234, 5643, 3445)

They are using an OLAP software package from COGNOS and are not proficient enough in Oracle to be able to use package functions. Their SQL is generated by the software package via their column selections and criteria settings from the OLAP tool.

Any thoughts?