Like the second poster, I feel that quality is the most important issue when considering this type of ad. There is a big danger of presenting an overly "corny", unintentionally low-class image of the business if the performance of the rap is poor or in bad taste.
Using rap is not bad taste in itself, no more than using Aerosmith or Maroon 5 music in an ad.
If standing out and making a memorable impression is the goal of a performance ad like the one described here, then it's possible that even a bad performance can do the job of creating an impression. The question is - will the lasting impression also lead to sales?