As far as I’m aware there aren’t any real problems reporting from AS400. There are solutions available for just about anything you can think of (some are even free). You can access data using ODBC to allow reporting from another platform (windows/linux/etc). It’s also possible to create .PDF, .XLS, .XML, etc files for export to other systems. The possibilities are (almost) unlimited.
There maybe problems configuring certain printers to work correctly from an AS/400, but that’s normally just down to the experience of the support staff doing the configuration – once you know the correct settings it’s no problem. Network (IP) printers are also supported (with the right configuration of course).