For what it's worth. I solved this on my development version of OpenLP. Full disclosure: I'm not on the development team, but I have just finally set up the dev environment for OpenLP and I downloaded the current trunk from GIT.
Solution: in app.py, there seems to be an incomplete attempt to locate libvlc.dylib on a Mac, so I just tried to be more explicit about its location within VLC.app by adding the path within VLC.app: "Contents/MacOS/lib"
Code lines 548-555:
if getattr(sys, 'frozen', False):
...
vlc_dir = AppLocation.get_directory(AppLocation.AppDir) / 'vlc'
vlc_lib = None
if is_win():
vlc_lib = 'libvlc.dll'
elif is_macosx():
vlc_lib = 'Contents/MacOS/lib/libvlc.dylib'