Hi Brian ,
We don't believe there is a way to use BusyIndicator to indicate that the controls in your RadTabItems are loading. You could use it when portions of data are loaded in GridViews, SheduleView for example , like demonstrated in this demo. But multiple UserControls loading among with animation processing ( the RadBusyindicator's animation) - we don't believe this is possible in Silverlight.
However, this is more like a general SL question, not a "telerik controls specific" one, so I believe you could also search in other SL forums.
the Telerik team
Explore the entire Telerik portfolio by downloading the Ultimate Collection trial package. Get it now >>