Hmm.. i have a question. This may sound noob, but why would modchips be required if:
A) You're using the same media that it's supposed to work with
B) You're using the same file system it's supposed to work with
C) You're using a copy of a game that get's past Wii's protection.
  --- Or does this mean that your Wii is unprotected? xD (double meaning)
And question 2
How did you get a Wii rom to work on GC? I know that there are modchips, but isn't the whole interface different? Or is it like both interfaces are on there, just one is disabled the other enabled, and a simple code change can fix?
A)I will use DVDs here but the technique equally applies to most other media, on DVDs there is a bit of lead in that a normal burner can not burn (by design usually). This contains such wonders as the CSS encryption keys and other nice things. Some more determined people can modify drives to burn these sections (there were some doing the rounds pre-DeCSS) but this is fairly rare. Occasionally certain dyes and other unusual authentication mechanisms are used.
B)See A), there could be some sort of protection based on corrupt sectors I guess (several "DVD" discs use similar "protection" of late and the Amiga used it too), .
C)I do not quite follow but disc swap techniques are usually the first way (PS1, console region adaptors, the passme(2) for the DS and loads more), also A)'s answer chimes in again.
2)Wii rom to work on GC? I assume this is a typo and was supposed to be GC isos on a Wii. I do not know if anyone has suceeded in running GC isos on a Wii and depending on features/hardware emulated (versus GC hardware actually in the Wii) it may be more difficult too pull it off.
Oh and good to see people starting early on Wii hacking.