You can easily determine if your items will a ViewModelItems or a TabItems if you are following the MVVM patter. For instance the ItemsSource property will be set only to your TabControl which has the custom viewModel. This could be your first point of detecting the change.
However you can easily get the Containers (RadTabItems) which are generated for a particular items using the ItemContainerGenerator of the RadTabControl.
var container =
I hope this information helps. If this is not what you were looking for please provide us with a little more infrormation and example of your user case.