The question was a bit of an idea. So the glibc version in not known yet, but I'm highly confident that they will differ. A reindex could in theory be possible in most cases, but is a definite show stopper on some of our databases, because it would mean too much application downtime.
Keep in mind that you only need to reindex text-based indexes. Ints are still gonna int. So it might not be too bad.
