Sure is. The easy way is to make a Playlist of the songs you want to use in iTunes, then select that playlist from the media browser in iPhoto.
Problem there is you can't set a crossfade, so there's probably going to be few seconds of silence between the first and second song. How bad this is depends on the songs themselves (and how much silence is actually encoded as part of the track specifically).
The fairly-simple way to get a really professional sounding track is to take your songs into GarageBand and edit them together with a nice little crossfade then export them as a single track. Put that under your slideshow for a really nice soundtrack.