IBM wrote:AIX does not support the execution of binaries created on later releases or technology levels of AIX on an earlier release or technology level of AIX. For example, execution of binaries created on the AIX V7.1 operating system (OS) would not be supported on a system running AIX V6.1 OS.
So this limits your question to specifically whether AIX 3/4/5.x 64 bit compiled binaries can run on a similar or greater version/TL LPAR 32 bit. I don't see anything that explicitly states it won't work in the compatibility notes, however I truly would not expect it to. One of the main header files nrpe relies on (stdio.h) doesn't seem to me like it would be cross architecture friendly. All I could advise would be that you're welcome to test and see if it works. I wouldn't get my hopes up though.