Much like a 4 GiB SD (nonHC) card, they're breaking the standard, so it may or may not work.

However, since the SDXC standard is pretty much just a way for Microsoft to make more money (SDXC is basically a filesystem swap), one would need to actively try to break > 32 GiB SD cards not using exFAT in order to break compatibility (or just be a sloppy coder). IMHO, of course.