OmniOutliner is a LinkBack client in 3.6, yes. This means you can copy in selections from OmniGraffle, and other
LinkBack aware applications and then double-click the attachment in OO to have it open in the right originating application for further editing.
But yeah, it would be cool to have OO be a LinkBack server too. With limited time, we felt that that embedding cool graphs and such in OO was the better first step.