Symbolic linking to Photos from another user
The iPhoto library is a package container not really a single file.  There are .plist, .db and other files in the package that might get altered differentially when you open via the different accounts.  This might contribute to the problems people mentioned.  Crazy idea, and I haven't tried it, but it might be better to recreate the package content on the new account using symbolic links to the folders that contain the actual photos on the old account.  This way all the .plist, .db and related files in the package can remain local to the new account, but you accomplish your goal of not copying the actual photos.  I definitely would back up the library before giving this a try.