The metadata lives in the database which is usually located in $HOME/.local/share/shotwell/photo.db. If you backup that together with your images that sould be fine, you just have to make sure that you use the exact same paths if you restore, otherwise things will get very ulgy
Additionally Is there anyway to host a centralized Shotwell for multiple people to access and dump images into?
People have tried to move the library on a share, for example. There are several issues that make importing to network shares not work very well. Also there is absolutely no protection whatsoever for concurrent access, so your mileage may vary.