Gollum/Smeagol are both actually quite clever. If the [minor The Hobbit spoilers] riddle scene in The Hobbit tells us anything, it's certainly at least that much.
So it stands to reason that the split-personality hobbit could also string a few clever rap verses together. And just wait until Smeagol starts dropping the bass.
But I'm not so sure I wanted to see his gnarly, toothy grin while he licks down an ice cream cone. Oh, the horror.