Ermat Zimm was a Bajoran artist.

In 2371, Quark used a portrait of Deep Space 9 that Ermat had drawn on several inscription pens he was selling during the Gratitude Festival. (DS9: "Fascination")

This character was only mentioned in dialogue.
According to the Star Trek: Deep Space Nine Companion and the Star Trek Encyclopedia (4th ed., vol. 1, p. 250), Ermat Zimm was an in-joke reference to DS9 production designer Herman Zimmerman.