Lots and lots of conjecture on ITB and rolling and what it does and what it doesn't do...
It's fair to say that your ITB has the same strenght as soft steel and so doesn't stretch much. It's lenght can be influenced by doing stuff to TFL at the top, or the lateral retinaculum at the bottom.
No idea how rolling your ITB (or the deeper VL) works, but it does a pretty good job in relieving some knee and some back pain. It's only ever a pain reliever, never a cause changer.
There is a big correlation between functional control (and not strength) of glut med. The less control the more pain there is on rolling ITB...