I have a Windows laptop and my spouse has a Mac. Is it possible to share the photo library? The pictures would be stored on a network attached hard drive accessible to both Mac and PC.
This isn't a complete answer, more a heads-up on a potential trap.
WLPG will certainly work with photos on a network-attached hard drive. So if iPhoto will do the same, then in theory you can share the photo library. Not having a Mac or iPhoto, I can't confirm this.
However, be aware that WLPG stores Tags (Keywords) as XMP-based metadata into the images themselves as well as in its database, whereas iPhoto only stores Keywords (Tags) into its own database. iPhoto doesn't know about XMP. This means that any work you do on tagging images on one platform will have to be duplicated on the other, in order to keep the Keywords/Tags in step. If your spouse also had WLPG, then the Tag hierarchy would automatically be kept in step on both machines, whichever machine was used to edit the Tags.
This may also be a useful post for you, by someone who has experience of using both programs.