Der Glockner von Notre Dame was directed by James Lapine who also did the book (Does this justify Disney for the Sondheim fans among us

). He didn't stick to the original movie script, but wrote a completely new book based on the original novel although he did stick to some of the changes that were made for the movie. Gringoire is still not in the musical. The gargoyles were written out of the musical, but later put back in because Disney felt the show lost to much of it's original power. The Gargoyles were renamed and by that the 'Victor-Hugo-joke' was cut.
In the end Disney felt the musical was too dark and didn't want to transfer to broadway. The theatre in Berlin was built for the musical and the sets used a lot of projections like Webber's The Woman in White did.
I recently saw a community theatre performance of Der Glockner staged in a church and it was incredible. This is absolutely one of Menken's best score ever. Especiale the first act finale where all the musical themes come together and clash. It gives me shivers everytime when I listen to the cd.