I'm not overly familiar with Juwel filters, but if it's jsut the stadard 'oh yes, it aerates the water' jobbie, then as long as the filter agitates the surface enough then no.
Hi, I have a Juwel tank. I have put in an airstone which I only run in the evening because A. I have a large Pleco and they appreciate the extra movement and B. I like the look of the bubbles! It isn't essential to have one but it's nice.