The mindset of AS/400 developers is the least of your problems.
AS/400 does not integrate happily over modern interfaces such as ADO.Net. To integrate AS/400 system with other environments, one needs to rely on crude text files or learn to live with the partial functionality that legacy ODBC and legacy ADO interfaces offer. Here are some rules of thumb for using SSIS 2005 to ETL data to and from AS/400 systems:
The calling of AS/400 Stored Procedures from SSIS has a few mysteries. Here is the solution that I eventually came up with - it consists of using typical OleDb objects and their usual gang of methods, all done in C#, with a smattering of VB script to glue the whole C# assembly into SSIS 2005.