It depends on what you're trying to do.

If you plan to build a new wheel on each machine, you'll need to configure the OpenBLAS paths any time they're not in a standard location (probably /usr/lib).

If you are planning to build the wheel once and install it multiple places, there are tools to include externally-built libraries: the scikit-build-core docs list auditwheel for Linux, delocate for Mac, and delvewheel for Windows, with cibuildwheel for automating the process of building and testing the wheel, and the new repairwheel to pick the relevant command of auditwhel, delocate, and delvewheel to run. SciPy has a similar issue open, which mentions some of the same tools.

There is also the possibility of using a package manager like conda that can handle non-python dependencies: it looks like NumPy, at least, has a ppc64le build available.

The question seems answered (thanks @DWesl!), so I will go ahead and close this issue. Follow-up questions are still welcome of course.