I doubt that delving into libxml code is going to help you much unfortunately. Let us know what you find out.
No, it didn't, but it did actually lead me closer to the problem. It seems that Maya has its own xml2 library, libawxml2.so, which is colliding with the xml2 that's linked into the plugin. It is sufficiently different that I can't just not link in xml2, though. It surprises me that a collision like this isn't being detected, but there it is.
I'll have to either find header files, so I can compile collada against them or figure a way to get the plugin to call the functions included within rather than going externally. Maybe I can figure out a way to static link it in or something.