While Painter does not have a Smart Blur filter, a similar effect can be achieved with the Effects: Focus: Glass Distortion effect. By selecting Image Luminance from the Using pop-up list, you can choke and spread the light and dark areas of an image. Choke refers to shrinking areas of density within an image; Spread refers to expanding areas. You can use the Invert checkbox to reverse the effect of Choke/Spread.
The application of Glass Distortion to a photograph is not the same as Smart Blur, but it does tend to drain an image of its complexity. You can experiment with the Amount slider to either exaggerate or reduce the Choke/Spread effect.
Viva la Painter!