You do not add things to the exclude list.. you only exclude things that are by default excluded.. if there is nothing on the list it is included. It is kind of inverted thinking.
If the iphoto library is on your normal OS disk it is included.
Why do you think it is excluded?
Is it installed on a different disk? That disk has to be HFS+ format to be included in the TM backup.
It has to be local disk not network disk.. TM cannot backup network disks.
You can "see" the iPhoto library in Time Machine backups, but you cannot "open" the library or "browse" the contents while you are in Time Machine.
Apple makes you restore the entire iPhoto library to another destination...like your desktop....if you want to retrieve a few older images that you may have deleted by mistake.
This is a convoluted mess, but unfortunately, that is the way it is.
See Pondini's excellent, detailed information on this:
You might also want to post in the iPhoto support area to see if the experts over there might have a workaround for you. I cannot find one, but I'm not an iPhoto expert.