If you're running Lion or later the Home/Library folder is invisible and that's where the domian files are located. That folder will be invisible in the TM backups also. Therefore you can extract Domain files one at a time out of the TM backups for import into iPhoto. You would do it as follows:
1 - download and run Find Any File to search for a file named ".site".
FAF can search areas that Spotlight can't like invisible folders, system folders and packages.
2 - the search can take a while due to the structure of the TM backups.
3 - select the backup from which you want to recover the Domain file.

4 - drag the file from the search results window to the Desktop.
If you recover more than one Domain file be sure to rename them after dragging to the Desktop so that you don't overwrite one with the next.
5 - you can put the Domain file(s) in your Home/LIbrary/Application Support/iWeb folder but will have to make the library visible as follows:
NOTE: In Lion and Mountain Lion the Home/Library folder is now invisible. To make it permanently visible in Lion or Mt. Lionenter the following in the Terminal application window: chflags nohidden ~/Library and press the Return key - 10.7: Un-hide the User Library folder.
For Mavericks, 10.9, go to your Home folder and use the View ➙ Show View Optionsmenu to bring the this window:

To open your domain file in Lion or Mountain Lion or to switch between multiple domain files Cyclosaurus has provided us with the following script that you can make into an Applescript application with Script Editor. Open Script Editor, copy and paste the script below into Script Editor's window and save as an application.
do shell script "/usr/bin/defaults write com.apple.iWeb iWebDefaultsDocumentPath -boolean no"delay 1
tell application "iWeb" to activate
You can download an already compiled version with this link: iWeb Switch Domain.
Just launch the application, find and select the domain file in your Home/Library/Application Support/iWeb folder that you want to open and it will open with iWeb. It modifies the iWeb preference file each time it's launched so one can switch between domain files.
WARNING: iWeb Switch Domain will overwrite an existing Domain.sites2 file if you select to create a new domain in the same folder. So rename your domain files once they've been created to something other than the default name.
OT