Installed CIOSes patched as per your link and all working perfectly. Wii games saving to emuNAND on hidden HDD all fine. GC via Nintendont also has working saves (well, as working as I ever get them to be). Tested on both original Wii and WiiU vWii.i believe so. @XFlak do you agree?
Thanks so much for your help, @fledge68 , @blackb0x (looks like nothing for you to do, was CIOS), and @XFlak (modded FAT.app probably is a worthy addition to ModMii, as you say).