Export iPhoto library onto Time Machine?
Time Machine automatically copies everything on your user folder, so you don't have to manually drag your iPhoto library to your external drive to back it up. Unless of course you have excluded some files or folders on the Time Machine preference pane, in which case no backups of such resources are being made.

In order to see the library on your Time Machine backup, you would have to mount your .sparsebundle and then look for it, and it does not seem to be the case.