Mac OS X actually has a bunch of structures that can conceivably be called libraries. There's the closest equivalent to the Windows DLL - the UNIX-style SO (shared object); the bundle, and the framework (both of which have no Windows equivalent). All of these things can be probed to find their exported functions and dependencies, but I don't know exactly how it's done.
You could also try the new MacDependency which shows all dependencies in a hierarchy as well as the symbols exported by the dependent files. It is open source and you can get it from http://code.google.com/p/macdependency/