Probably not - it is unlikely that any cloud backup will work for your iPhoto library at this time - the iPhotolibrary gets giant and must be on a drive formatted Mac OS extended (jpournaled) - no one has reported success with cloud backups and many people have reported failure - At least have a local external hard drive backup too if you are going to use the cloud
I take it you drag your pictures folder to DropBox, in most cases you will be able to see the pictures unless you open the iPhoto library. You need to control click on the library then select show contents then double click on masters, select the year folder then select the folder. You should make sure this folder is setup to sync this will make sure you have the latest update to your photos. Take a look at this link, https://www.dropbox.com/help/175/en
Something to take into account with Cloud back up:
How long will it take you to upload 51 gigs of data?
How long will it take you to download 51 gigs of data? Then factor in the load shaping that services use, so that their system isn't overwhelmed? We've seen reports on here of people taking days to restore a back up.