You do, for a split second. Once LV has kicked in (1 second) AE-L (hold) re-engages on its own. So, switching from Viewfinder to LV doesn't turn AE-L (hold) off at all. The second that it takes to full engage is how you lock the camera, or it locks itself, before it can do anything insane with the ISO and shutter.
Try it out.
Try it out.