FWIW, my Gemini-formatted 256GB SD card worked fine with my Mac.
(Which is more than can be said for the Gemini itself…)
Yes, because the Mac also reads FAT32.
However:
If you took a new 256GB SDXC card out of the package, wrote data to it on the Mac (without re-formatting the card), you would not be able to see that data in the Gemini, which would demand re-formatting it.
If you place that 256GB card into most modern digital cameras, they will demand re-formatting it back to ExFAT, which will no longer work in the Gemini.
The 'official' format for SDXC media is ExFAT.
My Nook HD 9" tablet, Galaxy Note 3 phone, Pandora console, Pentax Optio W camera are all 4+ years old. They can all read ExFAT. The fact that the Gemini will not use ExFAT, but claims SDXC compatibility, makes it's inability to read ExFAT a bug.
I'm actually not a big fan of ExFAT. But, I'm even less a fan of FAT32.