For CFG you don't need a SD card. I haven't used NeoGamma or any other loader, but, as for CFG, if you followed ModMii's guide, you should have its folder in your USB (FAT32 partition) root. So far, I managed to run many apps (WiiXplorer, Savegames Manager, MMM, CFG loader etc.) without a SD card. I just can't run HomeBrew Browser (with ou without a SD card yet). Everything else is running flawless.
But I'd like to ask the same thing Zod asked. What's the difference between the cIOS? Should I update if no game showed any problem so far? If so, how should I proceed? (I tried copying them to the SD card and using WAD Manager in MMM but I get an error, probably because I already have cIOS249/250?)