As far as I can tell, people have managed to get SDL apps to work on the Wii. I don't know how they went about this, though. They may not have even used SDL. The "partial port" linked to doesn't include the core SDL library, which is what OpenJazz uses.

Because OpenJazz restricts itself to SDL (and optionally libmodplug), the existing ports were fairly straightforward. So if there is a straightforward way of porting SDL apps to the Wii, someone else will probably port it sooner or later. If it's not straightforward, it would be difficult for me to do it myself.

"myself": OpenJazz should be compiled as C, libmodplug should be compiled as C++. There's no need to compile them as the same language.