I don't see any problem with this advert at all. The position that it's an affront to an ethnic group- intentional or not- is cynical bordering on the absurd, and in my opinion indicates a predication on the part of the offended to being offended.
The rhyme is neat and the accent makes it funny-- but don't go pretending people are laughing at the accent as a base mockery, because they aren't.
I'm probably wasting my time, but if you can't stand the heat, stay off the sofa. Whiners and moaners ruin it for people who're quite accustomed to and even enjoy the real world, where humour and creativity isn't limited to the gender/colour/nationality neutral.
~ The Jibblies.