Ok, after a few recompiles with different libraries available I came to the following conclusion:
C::B will not compile against WxWidgets 3.0.x, at least not yet. So everything I said previously that related to that, ignore it.
HOWEVER, having zlib-1.2.8 installed in /usr/local will cause compiling C::B to fail, specifically the help_plugin is where it bombs complaining about gzopen64. As soon as I remove that library, C::B compiles just fine.
So I think it's safe to say that C::B does somewhere use that library, but fails when it comes to linking to it and I suspect because when it tries to link using -lz, it's trying to link against the system installed one, and not the newer one. And since the system one (1.2.3) does not have gzopen64, it fails.
So there you have it. I think I have now tried compiling C::B well over a dozen times, some with success, most not. As I said in my previous post, for the purpose of getting the rpm compiled and installed, that has been successful (but only after I removed all of my custom libraries from /usr/local.)