Both the PA-RISC 2.0 and Itanium 2 binary depot packages are created using the same packaging mechanism, but they are built on completely different architectures.
The PA-RISC binary depots are built on a PA-RISC 2.0 machine running PA-RISC HP-UX 11.11, 11.23 or 11.31 and, in most cases, can be swinstall'ed (and run OK) on an equivalent Itanium 11.23 or 11.31 machine by adding "-x allow_incompatible=true" to the swinstall options on the Itanium 11.23 or 11.31 machine.
This is only possible because Itanium machines can execute PA-RISC code via emulation built into the Itanium HP-UX operating system. Similarly, it should also be possible to install/run PA-RISC 11.00 or PA-RISC 11.11 depots on PA-RISC 11.23/11.31 or Itanium 11.23/11.31 systems via the additional -x flag documented above.
The Itanium binary depots are built on an Itanium 2 machine running Itanium HP-UX 11.23 or 11.31 and cannot be run on any PA-RISC machine.