If there are people in the image that are readily identifiable, yes. This is true for any image that will be used in promotion of something else. In your case things become a little muddy and ultimately comes down to the, "what-if?"
"What-if," the street performer walked into an office and saw a photo of him/herself and thought, "I never signed a model release for that. Dang, I'm ticked off!" and then proceeded to find a lawyer, hunt you down and drag you to court. Then the judge happened to be haunted by a terrible school photo from his early childhood and was like, "this court finds that you owe street-performer cash for mental anguish!" Probably will never happen.
As photographers we are allowed to photograph anyone and anything we can see with our naked eye on or from public property. This law stems from the protection of press freedoms and extends through freedom of speech. In this regard, to make a photograph of a public performance artist in a public place and then charge money for prints, you do not need a model release. However, you should always have a model release with you. You never know when you will find that amazing image that Coca-Cola wants to pay you 10k for.
*of special note...when photographing a piece of public art wherein the art is the central focus of the image, you do need permission from the artist to resale the image. However, if the artwork appears in the image as a part of your composition, you're alright.