From Weston W. Fields:
It is further stated that Rabbi Akiba said: "God forbid!-no man in Israel ever disputed about the Song of Songs (that he should say) that it does not render the hands unclean, for all the ages are not worth the day on which the Song of Songs was given to Israel; for all the Writings are holy, but the Song of Songs is the Holy of Holies."30 This is to some an indication that Rabbi Akiba interpreted the Song allegorically. It is true that it is difficult to understand his hyperbolic language if he did not.
Field's entire article can be found here: http://faculty.gordon.edu/hu/bi/Ted_Hildebrandt/OTeSources/22-SongOfSongs/Text/Articles/Fields-SongOfSongs-GTJ.htm
See also http://www.chabad.org/library/bible_cdo/aid/16445/showrashi/true