We have not yet created a Legend control to work with the RadChartView, but we have plans to introduce one for the next official release. Most probably it will be a stand alone control which you will be able to place wherever you like, and it will not be a part of the chart's template.
I suggest you follow this approach, too. Create a user control (or a custom control if really needed) that wraps two controls - the chart on left and the legend on the right. You can expose a property Chart (type RadCartesianChart) of this control and manipulate the chart from this property. Retemplating the chartview would not work because the chart internally works with its full size and not the size of the Grid in its template.
the Telerik team