Linux has mostly transitioned to little endian on PowerPC. AIX remains big endian.
AFAIK, this is probably the easiest way to test BE on hardware (if you need that for some reason) - NetBSD on a Raspberry Pi running in BE mode is easy to use. (EDIT: Actually the more important thing is that it's cheap and easy to acquire)
Otherwise you don't need the other endian to confirm it?
Or are you saying to test their software before it goes out to big endian devices, which doesn't answer the question as to why someone would want to use it on those end devices?
I don't know whether this logic applies to this specific sort of bug, but there is a long history of bugs that "don't matter" combining with other bugs to become something that matters. Therac-25 was a bug that didn't matter on the hardware it was developed for, but then the software that "worked fine" got repurposed for another hardware platform and people died. If there's an easy way to identify an entire class of bugs it seems like a good idea to do it.