ROOT will search for some requested shared library in the “ROOT_LIBRARY_PATH”. Still, this variable will NOT be used by the dynamic linker to find and load other shared libraries that your requested shared library depends on. The dynamic linker will only see shared libraries in the “LD_LIBRARY_PATH” (and “RPATH” and “RUNPATH” set in your requested shared library, of course).
See also (try the “brutal fix”):
BTW. You also mention the “ROOT_LIBRARY_DIR” variable, but this is a configure/compile-time variable, not a run-time one.