Yes and no. While I believe it would be possible to point each accounts instance of iPhoto to the same library, in the likely event the library was launched on two accounts at once it could be corrupted or worse.
A better solution (available in iPhoto 08 at least) is to open up the iPhoto preferences and enable sharing so the library can be viewed on any account or computer running iPhoto on your network.
Alternatively, you can setup your own file system independent of ipHoto where photos can be available to all accounts on the machine. In this situation, you would lose the ability to manage your photos with iPhoto altogether, but would be able to skip the hassle of setting up a shared library.