If you're wanting to use ninfs to remove the verification in order to transfer your data, then idk how that's done. You should just dump your DSiWare from your SD card.
Follow this guide here: https://dsi.cfw.guide/
Yes, they're compatible with DS emulators.
DSiWare saves are generated on the SD card, instead of internally on the NAND.
They should also be usable with emulators.
Older nds-bootstrap versions which didn't have the slowdown would cause multiplayer games to have communication errors. Because of that, later versions added the slowdown to fix/reduce the errors.
While it should be possible to remove the slowdown just for C-Gear usage, it is unknown how to do...