Hi James,
I'm not sure where it's taking those legends from, and as I said there are quite a few missing attributes/properties in the current implementation of the Charts. According to this demo for example (view the XAML to see), the Legend text is set no the DataSeries, and looking at the Gizmox's Charts code, the property is not rendered at all.
I'm sorry, but I don't see a way to make it work with the current implementation of the Gizmox control. The Legend shown on the chart must be something that Visifire automatically puts there, or that's my assumption at least.
Palli