This is not an exhaustive list but some thoughts on the pros and cons of running OSS in different environments found on Power Processors.

IBM i and AIX both baked into the OS Kernel on Power CPU
No separate OS IBM has to update the kernel code to latest AIX, so you might be delayed getting the latest AIX
OSS has been ported over by Michael Perzl, bullfreeware, and aixtoolbox OSS is typically developed for Linux and Intel (Little Endian) first
Forks of processes are slower
IBM I and a Separate Linux LPAR on Power CPU
Another OS to patch and upgrade
OSS is typically developed for Linux and Intel (Little  Endian) first Compiling OSS from source might have to be modified to work on little endian Power CPU
OSS packages are available to download via YUM or APT-GET? Have to carve up a Separate LPAR allocations of disk, memory, cpu
There is free versions of Linux but most enterprises will probably go for paying a license to RHEL or SUSE for support and stable releases