This should be per appointment logic. 

Currently this scenario can be achieved by customizing the default Appointment ControlTemplate. The exact approach is explained in the following article from the help documentation:

http://www.telerik.com/help/silverlight/radscheduleview-howto-remove-delete-button.html

A sample project can be found in our XAML SDK repository:

https://github.com/telerik/xaml-sdk/tree/master/ScheduleView/RemoveDeleteButton