Emulator

I recently purchased a used 4GB non-HC SD card (there are still 6 available from this seller if you need one for testing):
https://www.ebay.com/itm/155830965023

Dumping it and using in Dolphin straight-up does not work while doing the exact same process on a 2GB non-HC SD card (such as the one that came with the launch 3DS) does indeed work

The thing is though, I can confirm that this 4GB non-HC SD card mostly "just works" on a real Wii console's Wii Menu with its data management and the SD card menu and the like, and can also similarly confirm that mostly "just works" in Excite Truck (even launched from the commercial disc!) with its custom soundtrack function working which, being a Wii launch title, does not support SDHC cards.

The reason I say "mostly" is because there's an odd quirk with regards to transitioning to and from the Wii Menu on real hardware:

Insert 4GB non-HC SD card ▶ power-on console to Wii Menu ▶ launch Excite Truck disc — custom music "just works" ▶ return to Wii Menu — "Data Management" does not work ▶ eject and re-insert 4GB non-HC SD card — "Data Management" works

Insert 4GB non-HC SD card ▶ power-on console to Wii Menu — "Data Management" does not work ▶ eject and re-insert 4GB non-HC SD card — "Data Management" works

Power-on console to Wii Menu ▶ Insert 4GB non-HC SD card — "Data Management" works ▶ launch Excite Truck disc — custom music does not work ▶ eject and re-insert 4GB non-HC SD card — custom music works

If you turn on the console with the 4GB non-HC SD card already inserted and then run Excite Truck, everything "just works". If you then exit to the Wii Menu, you need to eject and re-insert the 4GB non-HC SD card in order for the Wii Menu's data management to properly see it. Similarly, if you boot with the console with no SD card and, while on the Wii Menu, insert the 4GB non-HC SD card, it'll "just work" in the Wii Menu's "data management" but subsequently launching Excite Truck results in the card not being seen unless you eject and re-insert it.

Curiously, BootMii as boot2 on my launch-day Wii does not work with a 4GB non-HC SD card (which is unfortunate since I normally use USB Loader GX's custom ppcboot.elf to boot directly into USB Loader GX). However, all other homebrew I've tested seems to work without issue (Homebrew Channel, Not64, USB Loader GX, WiiXplorer).

FAT16 vs FAT32 did not seem to make a difference in any of this stuff. Also, I can make a video recording demonstrating any and/or all of this if you'd like.

Inside of the following 7z archive are 4 disk images of my 4GB non-HC SD card, two in FAT16 and two in FAT32. The "empty" ones are self-explanatory while the ones "with data" have a single license-free MP3 you can use for testing as well as my completed Excite Truck save data pre-configured to use custom MP3s; also included is USB Loader GX and the aforementioned custom ppcboot.elf to demonstrate how bootmii unfortunately does not work while USB Loader GX itself does:

http://0x0.st/Hktp.7z

And to make it easier for testing in Dolphin, I've attached a stand-alone copy of that very same completed Excite Truck save data of mine pre-configured to use custom MP3s.