Still, you won't be able to "fix" anything with the compiled libraries. You might be able to disassemble object files to analyse what functions are doing but this would be illegal to use back in open-source library and might be harder to do than you guess it is. What is needed is the source code of library which is off course not even available to official devs.
As far as compiling homebrew with official sdk to get wiimotion plus support in existing apps, this is going to be very complicated as you would need to rewrite quite a lof of things in those apps to make them support official API instead of libogc, the compiling process might not be that easy (if even possible on a personal dev environment ?) and finally, there is no guarantee that produced binary (are those even .dol ?) could run on retail Wii, I imagine you need a DEV unit to run those files and maybe also a license dongle on your PC to compile/send the binary.
Really, the only interesting stuff in those leaked SDK is the documentation and even that only for the purpose of reading stuff that you weren't supposed to read, I'm pretty sure homebrew devs know all the important stuff already, as libogc is very complete and very similar.
Maybe someone could try to compile liboc stuff with metrowerks compiler to see if it produces more optimized code than gcc (probably the case) but in 6 years, nobody seems to have been able to do it, I doubt it will change today.