This snippet of code gets the process created and sets the parent as the main window. It looks like the child application lives within the pane, but when switch to other RadPanes (tabs) via mouse click, the child application is still the foremost view.
testChildapp = System.Diagnostics.Process.Start(process);
_appWin = testChildapp.MainWindowHandle;
var parent = new WindowInteropHelper(Window.GetWindow((TestAppPane.Content));
SetWindowLongA(_appWin, GWL_STYLE, WS_VISIBLE);
MoveWindow(_appWin, 200, 100, 200, 200, true);