And if not wrapper then compression which is treated much the same in most cases. It could be that the dev was writing for multiple systems and those are the n
ube flavour (the wii was basically an overclocked gamecube after all and the Wii versions might have followed one from there) but that would matter more if you are comparing the releases between platforms.
After that I find it will typically be one of two things
1) The dev wrote an archive format handler and decided to put everything through it, even if there is an established handling method.
2) The dev wrote an archive format and used it for them.
Those do not look like the normal GC/Wii 3d model formats (BMD would be the extension there, http://hitmen.c02.at/files/yagcd/yagcd/chap15.html#sec15 http://wiki.tockdom.com/wiki/BMD_and_BDL_%28File_Format%29
with variations on the theme also seen on the DS where it is more commonly known as NSBMD and now also the 3ds and wii u) , however they were hardly universally used. Not sure what we have as a Wii 3d hardware reference, it would probably have to be read http://wiibrew.org/wiki/Wii_Hardware
for the basic overview and then jump into the source and wiki for https://dolphin-emu.org/
. It is probably going to be simple enough that you could piece it together from basic knowledge of 3d formats and the hardware (the wii straddled the line between high level format and useful for the hardware a lot of the time), and possibly also comparing other models in the game (hopefully there is a nice simple elementary shape as a bonus character or something).
If you were thinking "get this program/plugin and open it in maya/3ds max/blender" then that does not really exist outside of PC games modding and maybe something that uses unreal engine, certainly not in ROM hacking like we tend to see on the Wii and other systems around here. You can occasionally come the other way if dev tools have been leaked and get the specific version of maya/3ds max/blender used by the leaked stuff and make something from the ground up but I am not aware of any in this case.
Textures on the other hand you might be able to edit more easily, not sure offhand what level of normal/height/displacement mapping there would be in this game.